Trivia fact of the day. . .
Bulbs actually age with use, developing micropores in the glass and microscopic notches on the filaments, making the filaments increasingly likely to break. In an SEM, the tungsten filaments look like the "zebra stripes" visible here and over time they get deeper into the tungsten:
Since your bulbs were installed at the same time, when one fails, replace them both or you will begin a game of constantly replacing one and then the other. Same with turn signals or other left/right sets.