Prerequisite Tree (PRT)
The Prerequisite Tree is a TOC Thinking Process used to create implementation road maps. PRTs are visual diagrams describing the necessary condition relationships required to accomplish the desired objectives.
Prerequisite Trees are particularly useful when the final solution is clear, but the way forward seems blocked by obstacles, excuses and/or general confusion.
Prerequisite Trees are particularly useful when the final solution is clear, but the way forward seems blocked by obstacles, excuses and/or general confusion.
If you ever catch yourself objecting to a fundamentally sound approach (“but that’s not practical!”), it is time to map a Prerequisite Tree!
How the PRT fits into the TOC Thinking Processes
The Prerequisite Tree takes the complete set of injections (solution elements) from the Future Reality Tree and sets them as it’s “objectives.” It then breaks these objectives down into an ordered sequence of intermediate objectives (key milestones) for execution. Refer to Step 4 in the flowchart below:
Other Applications of the Prerequisite Tree
The Prerequisite Tree is a powerful and flexible implementation tool that can also be used for:
- Project planning
- Designing training programs
- Go to market strategies
- Defining business processes
- Personal development plans
- Execution planning
- Change management
When NOT to Create a Prerequisite Tree
A Prerequisite Tree is probably not required if you already have clear idea of what steps to take and what order to take them in. At such times, creating a PRT can be just another excuse to procrastinate. It is easy to fall into the trap of over-intellectualizing because the necessary actions seem uncomfortable, unpleasant or time consuming. Eat that frog!
How to Create a Prerequisite Tree
The steps to creating a Prerequisite Tree are:
Each step is explained in greater detail below. But first, a few general guidelines:
- Define the objective(s)
- Brainstorm the obstacles to achieving each objective
- Reverse each obstacle to form it’s Intermediate Objective (IO)
- Sequence the Intermediate Objectives in the correct order
Each step is explained in greater detail below. But first, a few general guidelines:
- Write each statement in the present tense, even though they do not yet exist (avoid using the word “will”). This puts you into the right mindset for dealing effectively with each obstacle.
- Be bold. Avoid tentative, wishy-washy statements by removing words like “might”, “possibly” or “maybe”
1. Define the Objective(s)
If you are using TOC Thinking Processes, your objectives are simply the full set of injections finalized in your Future Reality Tree. Other typical examples of objectives could be:
- I have my own YouTube channel
- Maintenance lead times are reduced 50%
- We have less than 2% stockouts of our products in retail outlets
- I am promoted to manager
- At least 70% of the prisoners from our facility are gainfully employed 3 months after release
- We always complete our projects on-time
2. Brainstorm the Obstacles to Achieving Each Objective
This is usually the easiest step because our brains find it easy to make excuses.
It is not necessary to think up every possible objective at this stage because you will probably continue to discover more in Step 4. But try to capture as many as you can.
Then cross-check each obstacle:
It is not necessary to think up every possible objective at this stage because you will probably continue to discover more in Step 4. But try to capture as many as you can.
Then cross-check each obstacle:
- Make sure it actually exists now
- It should be stated in terms of what does exist rather than what doesn’t exist / what is missing
- Confirm that it actually blocks you from achieving the objective
3. Reverse Each Obstacle to Form an Intermediate Objective (IO)
The Intermediate Objective should either eliminate the obstacle completely or neutralize it by making it irrelevant for achieving the objective.
It is usually possible to find more than one Intermediate Objective per obstacle. Choose one that:
It is usually possible to find more than one Intermediate Objective per obstacle. Choose one that:
- Overcomes the obstacle effectively
- Motivates you to implement it
- Makes the objective more doable
4. Sequence the Intermediate Objectives in the Correct Order
a. Start with two Intermediate Objectives that seem to have a dependency between them
b. Diagram them with the earlier item below and the later item above, connected with an up arrow indicating a necessary condition and the obstacle being overcome:
b. Diagram them with the earlier item below and the later item above, connected with an up arrow indicating a necessary condition and the obstacle being overcome:
c. Read it out loud “We cannot accomplish <Intermediate Objective 2> because of <Obstacle 1>."
d. If you are not fully convinced that <Obstacle 1> blocks <Intermediate Objective 2>, ask yourself why not. If you uncover more obstacles for <Intermediate Objective 2>, return to steps 2 and 3 above. In case you cannot find more obstacles, perhaps there is no dependency after all and these Intermediate Objectives can be done in parallel (return to 4a above)...
e. On the other hand, if it does seem convincing, confirm whether <Intermediate Objective 1> clears the obstacle by reading it out loud: “In order to accomplish <Intermediate Objective 2> I must <Intermediate Objective 1> because <Obstacle 1>”. If this statement sounds a bit off, return to 4c.
f. Repeat 4a. until you run out of obvious connections. With luck they may begin to merge or cluster together.
g. Connect the cluster and any remaining Intermediate objectives to the main objective and test them using 4c. etc. Not all of the IOs may have dependencies, and several may feed into the topmost objective. For example, notice the range of relationships visible in the generic Prerequisite Tree below:
d. If you are not fully convinced that <Obstacle 1> blocks <Intermediate Objective 2>, ask yourself why not. If you uncover more obstacles for <Intermediate Objective 2>, return to steps 2 and 3 above. In case you cannot find more obstacles, perhaps there is no dependency after all and these Intermediate Objectives can be done in parallel (return to 4a above)...
e. On the other hand, if it does seem convincing, confirm whether <Intermediate Objective 1> clears the obstacle by reading it out loud: “In order to accomplish <Intermediate Objective 2> I must <Intermediate Objective 1> because <Obstacle 1>”. If this statement sounds a bit off, return to 4c.
f. Repeat 4a. until you run out of obvious connections. With luck they may begin to merge or cluster together.
g. Connect the cluster and any remaining Intermediate objectives to the main objective and test them using 4c. etc. Not all of the IOs may have dependencies, and several may feed into the topmost objective. For example, notice the range of relationships visible in the generic Prerequisite Tree below:
h. Where there are multiple objectives, keep in mind that some may form IOs for other objectives, and other objectives may have IOs in common. Start with the objective that seems most difficult and/or slow to accomplish, then carefully fit the others in and around it in your diagram.
i. Ensure that your entry points at the bottom of the Prerequisite Tree seem actionable. If not, return to steps 2 and 3 above to brainstorm obstacles for achieving the entry points, then and generate their respective Intermediate Objectives.
Note that the obstacles for a given objective are relative and may vary from person to person. A very influential person may not even need to bother writing down many of the intermediate obstacles that would be major stumbling blocks for a less influential person.
i. Ensure that your entry points at the bottom of the Prerequisite Tree seem actionable. If not, return to steps 2 and 3 above to brainstorm obstacles for achieving the entry points, then and generate their respective Intermediate Objectives.
Note that the obstacles for a given objective are relative and may vary from person to person. A very influential person may not even need to bother writing down many of the intermediate obstacles that would be major stumbling blocks for a less influential person.
Next Steps
Congratulations, you have defined a clear path to achieving your objectives! You have determined what needs to happen and the general sequence that it needs to happen in.
But you have not yet defined the necessary tasks, assigned resources, and set appropriate timelines for implementing the roadmap that you have laid out. You may wish to create a Transition Tree to break down the Intermediate Objectives further into more granular tasks and actions. You might also consider implementing Critical Chain Project Management to factor in resource availability across multiple projects and improve the likelihood of implementing on-time.
But you have not yet defined the necessary tasks, assigned resources, and set appropriate timelines for implementing the roadmap that you have laid out. You may wish to create a Transition Tree to break down the Intermediate Objectives further into more granular tasks and actions. You might also consider implementing Critical Chain Project Management to factor in resource availability across multiple projects and improve the likelihood of implementing on-time.