You pull into the garage on a cold October evening and notice it: rust bubbling along the bottom panel where road salt and slush have been splashing all winter, or a wood door that's swollen enough to stick halfway up the track. Maybe the aluminum trim panel has a dent from a stray snow shovel, or the seams on an old steel door have started to separate after one too many freeze-thaw cycles. That moment of "what is this door even made of, and should I replace it with the same thing" is exactly when it's worth comparing materials honestly, instead of just matching what was already there.