Theory of Constraints Handbook - James Cox Iii [662]
The S&T tree also has a sequence from left to right in a level. A step that is to the right of another step in the same level of the S&T tree cannot be implemented before the step to the left of it on the same level has started being implemented. The timing of when to start implementing a specific tactic needs to be based on logic. In some S&T trees, there is content in the step that points out when to start implementing the tactics.
Each step in the S&T tree includes some or all of the following statements in this order: necessary assumption(s), strategy, parallel assumption(s), tactic(s), and sufficient assumption. The NAs explain why the step is necessary (as part of the group of steps on this level that correspond to the step in the level above) to achieve the higher-level corresponding step in the S&T tree. Therefore, there are NAs listed in each step except for the step that is Level 1 at the top of the S&T tree. The NAs need to be convincing that the action must be taken by pointing out the damage of not taking the action and/or the benefits of taking the action. The sequence of NAs is in order of the concerns that people will have. The NAs in Level 4 are focused on what is currently being done and the need to do it differently. The NAs in Level 5 are about the difficulty in doing the tactic in Level 4—the tactic we already agreed to do.
One way to better understand what an NA is results from an explanation of necessity-based logic and a visual aid. In a conflict, we understand from the Evaporating Cloud (EC) tool of Thinking Processes (TP) that a need is what is desired from a want. In other words, an action that we want to take is really focused on achieving some need. The connection between the need and the want is a necessary assumption, the explanation why this want will result in the need being achieved. It can be read as follows: “In order to achieve the FIGURE 34-3 How the NA connects one step of the S&T tree to another. The NAs are always generic. If the NAs we want to address are not generic, then we can devote a whole step in the S&T tree to exceptions. A step in an S&T tree can be just for a specific case. Another possible approach is to include exceptions in the PAs and the resulting tactics within a step already in the S&T tree. A strategy is what we want to achieve. It is not stated as an action, but rather as being current reality. The parallel assumptions are for checking that the tactic will achieve the strategy. The PAs need to tell us how to do it; they are the most important part of the S&T tree because they provide the logic. The PAs explain the whole logic of the tactic—why the tactic has a real chance of making the strategy a reality. There are no surprises allowed in a tactic. The PAs must explain why the tactic is needed and will result in the strategy being achieved. The PAs are written using cause-and-effect logic. They are written in the order that makes logical sense to reach the conclusion regarding what the tactic(s) must be. They are not written based on the sequence of the tactics. They are written so that the cause-and-effect logic is clearly presented. An entity (cause or effect) must be just one sentence. However, we can have more than one sentence in a PA when the next sentence is a comment. It is better to keep the comment as part of one PA; it will be shorter because some content will not have to be repeated. In addition, we can put both a cause and effect in a PA. In some cases, we have freedom where to put the assumption in the