Oh yeah, a mistake was definitely letting me operate our robot's arm/elevator...for some incredibly odd reason, the cover wasn't on the electronics board, and I moved the joystick for the arm, intending to move it out of the starting configuration...
Wrong joystick. I accidentally moved the elevator down, and rammed the fingers of our manipulator into the mess of wires. We untangle them, and I try again...and do the same thing
(I'm the reason the joysticks are now labeled)
And another thing...lathes and hacksaws don't mix. One of our mentors was using a hacksaw to trim something down on the lathe, the blade caught on the metal, and got totally bent into what resembled a lightning bolt. The he decided to do it again, and the same thing happened...I'm not sure why, but we handed him a brand new blade after that, and he managed to not break it (I don't even know why we let him have a second shot at it).
Moral of story: Hand tools should NOT meet machinery.