I've often ended up guessing what things do and messing things up.
One example is when I couldn't remember the difference between git checkout -b and git checkout -B, so in my infinite wisdom I decided to use -B because surely capital letters are better! Tried using it to switch back to a branch, and... Yeah, that was annoying.
What I said was not absolute nor complete. It only includes one set of things to be careful with. The f flag is another that you should be wary of using without understanding what it does.