If a decision is not checking off, then there is probably something you haven't done that is required for that decision.
Read the decision description carefully and make sure you have done everything. Also, take a look at your round tasks on the side of your screen when you are in the PPC dashboard, email campaigns page or the landing pages page. These round tasks will be things you must complete before being able to run the simulation.
If it is a review decision, then you many need to spend more time reviewing what it is asking you to review.
If you have tried all of this and the decision is still not checking off, please reach out to firstname.lastname@example.org.