Why should casting be avoided?

A cast (obviously enough) means you’re converting something from one type to another. When/if you do that, it raises the question “Why?” If you really want something to be a particular type, why didn’t you define it to be that type to start with? That’s not to say there’s never a reason to do such a conversion, but anytime it happens, it should prompt the question of whether you could re-design the code so the correct type was used throughout.