manicmike

This makes me think that some of us don't change the needle unless it breaks or bends. Needles do wear down, like a stylus in a record player. After a while it'll be blunt and give you problems.
Needles are very cheap, so this doesn't have to happen.
Just Googled this phrase "how often should I change my sewing machine needle?" and the first two results cobtained the phrase "Change your needles often" in the summary alone.

EDIT: They all say every few hours of sewing or after every project.