Possible failure mechanisms depend on what type of bulb it is. In general, failures caused by manufacturing defects show up quickly, and failures caused by wear get more common after some amount of run time or number of on-off cycles(see “bathtub curve”).
Even something like getting screwed in a quarter turn more or less can have an impact, as that could change the direction of forces on the filament in an incandescent bulb, or change heat dissipation in the ballast/driver of a LED bulb.
Even general manufacturing tolerances can have a big impact, an electrolytic capacitor might have a tolerance of -20% + 80%, when brand new, so if the failure mode is that capacitor drying out, and the circuit fails when the capacitor reaches say 30% below its nominal value, there can be a huge difference in time to failure depending on where it started.
Also different light bulbs in the fixture could get hotter, just because of the arrangement/position of them.
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