Last year I was just finishing off a job for an elderly couple (go every year) I was leaning on the vans door pillar with left hand, and then slammed shut the side sliding door forgetting to take out the left hand. I shut closed all the way with my thumb in it, when I opened the door, my thumb was DEEPLY gashed right on the knuckle very deep, it took months to heal up and now has a big ganglion on the scar.
Wont do that again in a hurry !
Like you said, your hands are your most valuable tool.