I learned the hard way (although it was cheap) about pre-flight checks. [&:]
Sent my Super Cup up with the antenna collapsed on the transmitter. Got about 150 feet away and the engine cut out and the plane nosed into the ground, breaking the firewall, gearbox, prop, and wing struts, and cracking the fuselage slightly.
It was a good training exercise that cost me about $20 bucks, and I'll never
(yeah right) make that mistake again. So I am grateful this occurred in such an insignificant way, rather than forgetting something on a balsa and plywood expensive plane.