Garage door springs has certain amount of cycles of operation after which they brake. Make sure to lubricate them to make it last longer. Do not try to replace them on your own, it's very dangerous!!!
Over time cable loop rusts and brakes due to humidity that stays down after rain or snow. Do not attempt to fix it yourself, they under extreme tension!!!!
Opener gear snaps because of age and unbalanced garage door, when springs not properly adjusted, it creates more pressure on opener gear and under heavy load it snaps. Fixable by changing gear itself or replacing whole opener.