Just recently, the light in my hallway went out, and since my younger brother is afraid of sleeping in the dark, this became an unnecessary problem. In order to calm him down, my dad went to the nearest hardware store to buy a brand new light bulb. He needed to make sure that the light bulb was the right size, so he took the old, burned out light bulb with him to compare. After finding the right size bulb, he paid for it and brought it back home. He then grabbed a nearby chair so that he could stand on to reach the empty socket where the bulb would go. He had me turn off the light switch, which would make sure that he would not get electrocuted while putting the bulb on or burned when it turns on. After less than 5 minutes, he is finished screwing in the bulb. We flip the switch to see if it works, and it does. My brother was now relieved. 
Question: How did the light bulb burn out?
From use.