It's difficult to let go of a favorite bra. Like a good friend, it offers you comfort and support when you need it most. Plus, finding one bra you actually like is such a long process, it's easy to hold onto those that fit you well for a little too long.
If you're anything like me, bras are in regular duty until the underwire pops out, and even then they might get a few more uses. (Tip: put duct tape over the wire to prevent scratches.) Putting up with almost any other garment for so long would be almost unthinkable.