Light bulb socket gets hot

The bulb gets jolted while the element is hot, causing the filament to break. This can be caused by a door slamming, children playing with a ball, wind rocking a hanging fixture, people jumping or dancing on the floor above...etc. The use of "cheap" quality light bulbs. Bad connection either in socket or in connections.  Never-the-less, I still find that the #1 cause for the above scenario is to be found further inside the bulb socket. The bulb needs to make contact at two points in order for it to work (see fig 1)- at the end (nipple) and on the threads of the bulb. Sometimes the "nipple" on one bulb is slightly bigger than the next.