You don't have to memorize openings in order to play chess! Nor do you have to memorize conventions to play bridge.

Conventional openings and bidding systems have arisen in these games just because they've been so hugely popular for so long, and because fans have written down much of what they've earned. You don't have to memorize the conventions in order to play the games. You only have to memorize them if you decide to engage in serious tournament play.

The only chess openings I've memorized are the Giuoco Piano and Ruy Lopez (which are quite similar). And yet I don't hesitate to start a game with d4 (pawn to queen 4), even though it precludes my playing either of the openings I've memorized. I simply rely on principles of development and create my own opening as I go along. I may unknowingly be reinventing a book opening in the process, but so what? Unless I'm playing in a tournament against good chess players who've memorized openings, it doesn't matter at all.

Back when I was teaching myself bridge, I read up on the Stayman and Blackwood conventions. By now I've forgotten everything I ever knew about bridge conventions; but it doesn't matter. If I sat down to a casual bridge game tonight, I'd just apologize for my ignorance and go with rules of thumb. I remember how to count the point value of my hand; I have a vague idea of how to convey that to my partner and how to interpret other players' bids; and I could stumble through. In a friendly game, it shouldn't matter. And if I later decide to start playing more regularly, it won't be hard to read up and refresh my memory on some of the fine points.

Chess and bridge are perfectly playable games, even if all you've memorized are the rules. Any further memorization beyond that is icing on the cake, and it's necessary only in serious (non-casual) games.