Fear of not knowing something

Not quite sure if this is a fit on HN. But I'll go ahead anyway. Dealing with the "fear of NOT knowing something". I have tried but failed. Many times I have started out on doing something only to find that I haven't the slightest idea what lies ahead of doing that "something" and end up quitting. Exit uncomfortable zone. I'm quite sure this is something that people commonly face.

So, share your experiences and how you have dealt with it with some real instances so I have something to look at and try it on my next "start" (I'm a software developer, quite relevant but not binding this question)