Sometimes we come to a cross roads in life where we face a big decision we just don't feel comfortable making. We waiver, we delay, we can't decide if we should or shouldn't. On the really big decisions we worry we are going to screw it up.
1) The 85% Rule. You don't have to be 100% certain, or even 100% ready. In fact, you probably never will be. This rule does not mean you rush rashly into a decision. It simply means that you don't let the perfect be the enemy of the good. You still need to do your research, think about what you want, game out the pros and cons, and examine your feelings. But if the only decisions you ever make are so easy that you don't feel even the slightest niggling doubt, you are probably only jumping at the safe opportunities. And that should be scary because some of the best opportunities require us to grow and stretch a bit beyond our comfort zone. Content yourself with being 85% certain, and when you get to 85% give yourself permission to act.
2) Catastrophe thinking or overthinking. This is often a consequence of trying to get to 100% certainty. Even when you have done your due diligence, you may feel you just aren't ready. You need more research, more planning. You let yourself get stuck in preparation for a leap you never make. Anxiety is the easiest way to recognize this problem. The solution is to get out from behind your computer, stop planning, and start doing. Get out of your house and go interact with people. Get a piece of paper and literally write down the worst case scenario. Once you get it on paper or say it out loud true catastrophe thinking reveals itself to be so silly that it melts away as a barrier. For me, catastrophe thinking made me believe I couldn't quit graduate school until I had a job lined up. It wasn't until my therapist pointed out that I could make more money working at Starbucks, and could just continue working my part time non-profit job that I finally felt the freedom to quit.
3) Sometimes not making a decision is itself a decision. If you can't decide between saying yes and saying no, if you wait long enough your opportunity to decide will be gone. That is ok, and rather than worry about your indecisiveness accept the fact that you are either not willing to make a decision at the moment, or are choosing to stick with the status quo. Which is actually a decision, so you were more decisive than you thought.