A large part of therapy can be pointing out cognitive distortions.
The idea that you need a bookshelf to last you for the rest of your life is actually a pretty reasonable thing for a therapist to question.
People come into therapy with a lot of strongly held ideas that wind up negatively impacting their relationships and lives. E.g. winding up in fights with your spouse because you insist on a bookshelf to last a lifetime, while they just want to get something reasonably priced and move on from the issue.
So trying to figure out where the desire comes from for an object that lasts a lifetime is actually a pretty reasonable therapeutic path of exploration. It's the old serenity prayer -- "the serenity to accept the things I cannot change, the courage to change the things I can, and the wisdom to know the difference".
There might be a lot of wisdom here in deciding that reasonably-priced bookshelves don't last a lifetime anymore, that that's not something you can change or want to spend time and effort on changing, and deciding you can finally be OK with that. To just make the choice to either buy a cheap one that doesn't last or an "overly expensive one" that does, accept it, and move on.