Man in the Funny Hat
Hero
Barring learning disabilities, only being involved in the game for a one-shot and then never coming back to it, or a DM who says that the rules just don't matter, no player has an excuse for not continually becoming ever more conversant with the rules for the game they're playing. Doesn't mean you are expected to MEMORIZE all the rules and never look anything up, but for a character you're actually playing over the course of a campaign, you are reasonably expected to know the rules that routinely apply to and are used by that character, and you should be paying enough attention to other rules (even if they don't apply directly to your PC) to soon enough become completely familiar with them as well.