We didn't have much money growing up, and I remember at least one Christmas where a single bulb had burnt out on the tree, interrupting the circuit and ruining the entire strip. We left cookies out for Santa but apparently he couldn't be bothered to rewire our lights. It was then I learned that Santa Claus is basically a lousy contractor who does the bare minimum of work required.
Nowadays even cheap Christmas lights are constructed in such a way that one bad bulb won't prevent the rest from getting juice. And for those of you that have forgotten what a technical marvel Christmas lights actually are, take a look at how they're made, and how they avoid lighting failure: