One interesting thing about life is the fact that there is no limit to number of times we can try things , if you try something and you fail at it , nothing to worry about, there is this great chance for Continually attempting it , till we get it right; you are not a failure until you fail to try again. You are not suppose to be discouraged and lose confidence in yourself when you fail, rather look for different strategies to get it rightly done. You shouldn't doubt yourself like, I don't think I can do this thing , because doubting our capabilities is a tool of self destruction , it will kill the zeal in us, and the next thing we see is giving up on ourself.
Doubt means to lack confidence in something, it can close you in and let fear controls you. Believe me the more you are captivated by the spirit of fear, the less you can stand for what you want. So also doubt is a time waster, because you'll keep pondering on the matters ( should i do it or stay back ). It will also do you no good rather it'll make you lose great opportunities, the only one thing you need to consider is the risk reward ratio, if it's something you know will be favourable then do it, and if it is not, stay away from it.
It is pertinent to know that doubt is a killer, you just have to know who you are and what you stand for. Always aim high, work hard and care deeply about what you believe in, when you stumble keep faith, don't give up. And when you are knocked down, get right back up, and never listen to anyone who says you can't or shouldn't go on.
My dear, life is very interesting and you can't afford to miss it. At the end, some of your greatest pain, becomes your greatest strengths if you believe in yourself, have dedication and that never quit attitude.
Remember champion keeps playing until they get it right.