Most people don't think much about their starter motor...until it stops. 

Car and truck starters have to deliver loads of torque for cranking vehicle engines in all conditions. In cold weather, battery drain and oil viscosity take their toll on the starter motor. In hot weather, starter heat soak can lock an iffy starter up. Either way, you're not getting anywhere if your starter motor decides to give up.

And don't forget about the battery cables. If the battery cables are dirty or corroded, they're making your starter's life harder too.