I check to make sure the bullets are tight from time to time, but that's it. The problem lies in the solder on the male end of the bullet to the motor wire on DJI motors. Their QC seemed to be lacking for quite some time causing motor failure when it heated up and for the lucky ones it was just a slight half second glitch in the motor.
Some people have said they don't like the quality of the bullets themselves but I haven't experienced any problems and I have unplugged them almost a dozen times now.
I know you are scared now, that feeling you had has been experienced by all of us at least once. Remember even the finest car in the world will have a mechanical problem, these flying contraptions are the same. Buy the best of the best and you aren't guaranteed to have trouble free flights.
Here is my scare! I still haven't got over this and anytime I hear something weird from my hex while in the air my heart drops. Typically it's just my GPS kicking up the motors to correct for wind... but I die a little everytime