I haven't played any Baldur's Gate games before but I've heard so much about this game that I'm going to buy it.

However, before I start, I always wonder about this: some games allow you to unlock any weapon at some point in the game, and if you miss one in some quest you can always go back. If you accidentally sell one you can buy it back or forge a new one again, or have it respawn. If you want some other class you can switch later.

Other games are not like that, and if you screw up or aren't aware of [full in the blank] then you can't unlock something.

What's the story with BG3? Do I need to be careful and plan before going on missions?