at one point in your life you will doubt something. Everyone has doubts and its the doubts thatmake us think even if we don't think properly and confidence is best at the time. It makes you rethink and state possibilities.
If you have doubts and something good comes from it then you learn a lesson. The same if something bad happens.
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But what about doubting someone, or doubting whether something will work out or not? Then I hope that you come with the great solution of just do it. You get one shot at life so go for it. Listen to your heart and listen to your brain. Some people say 'Think! Why would you do that?! Is your brain existing?!' Everyone has different views and oppinions so if someone thinks that they will go and I don't know, confess their love to someone you can't call them an idiot for believing that it was the right thing to do. Just remember that it's never to late. Yes that was a song quote. Deal with it.