Sometimes things in life does not work out and people say "Oh, I knew it... Why I've insisted?". We may speak it when we make a wrong decision at work, when we buy a sandwich and do not like the taste, and especially when the markets are not going in our favor.
The process decision making is a complicated task always associated with fears, insecurities, doubts and the refusal to accept the consequences. No matter how confident or full of self-esteem you are (and the ones that are too much, doubts are even greater), you will always have fear at this time. And you will deny any kind of external help just to feed your pride or you will try to find support in all possible external assistance to compensate for the lack of confidence in yourself (in the opposite situation). Both cases - not admit you have any doubts or leave your questions take away your part in the process - are terrible examples of how to make a good decision.
Also, there is a curious fact: these two characteristics, associated with fear of making a wrong decision will lead you to nowhere. You may lose an opportunity because you have not started soon or because you have started too late.
How to get around with it?
Admit you have questions. Doubt every decision that you are taking and do not rely on external comments. Stay comfortable enough to try to understand all the consequences that can happen if you take an action A or B. But, that's the main point, do not expect to have 100% of certainties to start. You will never be 100% sure, and not all of your certainties will be proven as true. Taking risks and acceptance of the consequences are parts of life. Admit it and move on!