I got it in my head when I was young that I had to pick up everything. I didn't want to be wasteful. I thought the game would think I didn't need that health, so it would quit giving it to me. So, I picked up everything whether I needed it or not.
To this day, I can't leave a health laying. A good example is in Metroid when you stand over those spawning holes for those beetle looking things. I shoot and shoot trying to get my missiles or health full. Even if I don't need what's dropped, I have to pick it up.