When one makes a decision, one needs to move on. Do not spend time reviewing it in your mind. Nothing good--and much bad--comes from going over past decisions.
Time spent on decisions already made means time is not being spent on decisions that need to be made. One has too much to do to focus on that already done. By fixating on the past, one lets the present and future suffer.
No decision is perfect--at least no decision I ever made was perfect. But I was perfectly comfortable basing a decision on the best available information and then moving on. Yet, when new information came along, when the facts changed and a decision could be changed, I did not hesitate to reverse course.
Over the years, for example, I resisted so-called "merit scholarships." I had seen first-hand the program only works if a few colleges engage in the practice (if all competing colleges have similar practices, students will obviously make the same choices they would have made without the scholarships, but the colleges will have less net tuition revenue with which to offer their programs).
Despite the entreaties of my dean of admissions to offer merit scholarships, therefore, I held out as long as possible. In my view, all of the students admitted to a particular college should be meritorious, and financial aid should be offered on a need basis to those who could not attend the college without assistance. However, when I found we were losing admitted students to colleges that were providing merit scholarships and to which we previously had not "lost" students, I relented and reversed course.
If the facts change, one needs to change decision; if they do not, leave the second-guessing to others (there will be plenty of those people around). Just do not be one of them. You will be more focused on the next decision you have to make, and you will sleep better--much better!