Because brass instruments don't have many fine parts on and they look durable, owners don't likely think of handling their instruments with good care.
When you put it on a desk forcefully, throw it on the floor in a case, sit on it carelessly…, then the piston of your instrument may get stuck!
Why does that happen though you don't see any big change on it?
There seems to be the cause in a specific and important part.
Let's check it out by an experiment.