Second guessing usually means when you predict something about the future. It basically means an anticipation on the outcome of the future. It also said that people usually second guess if they think the outcome of the future is going to be something negative. Many people have this gut feeling that their second guessing may come true and sometimes it does. You will come across many people that second guess so well that it seems like he has peeped into the future. Second guessing usually leads to second thoughts. When you decide upon something and you feel that something negative might happen, you may have second thoughts. Second thoughts basically means to rethink what was decided before.