Comparison makes a new pair of shoes feel old by lunch.

Nothing you own is new for long once you start looking sideways. The shoes were fine in the mirror at home; by third period somebody has a better pair and yours have quietly been downgraded without changing at all. What moved was not the shoes. It was the standard you measured them against, and that standard will keep moving.

When something you liked suddenly feels cheap, pause and ask what changed in the last hour. Usually you can name the exact person you saw. That does not make you petty, just human, and noticing it takes most of the sting out.