“This plan won’t work” starts a discussion. “You never think anything through” starts a war.

One sentence points at the plan; the other points at the person. Criticism aimed at a specific thing can be examined, agreed with, or fixed. Criticism aimed at character leaves nothing to do but defend, so the conversation stops being about the plan at all. Most escalation begins at exactly that switch from what you did to who you are.

Before you speak, check that your sentence contains a noun something can be done about. Name the step, the date, the number, the part. If you are angry enough that only the personal version will do, that is the moment to wait.