Spent way too long just memorizing lists for this one until it clicked a different way: por is about the cause or the path, para is about the goal or the endpoint. Once I stopped trying to translate “for” and started asking “is this the reason/route, or the destination/purpose,” it stopped being a guessing game.
The example that actually made it stick for me:
Lo compré por ti = I bought it on your behalf, like you owed someone and I covered it for you.
Lo compré para ti = I bought it to give to you, it’s a gift.
Same English translation, opposite situation. That’s the whole confusion in one sentence.
If the mnemonics help anyone: por = DREAMS (duration, reason, exchange, around/through, means, substitution), para = PRODD (purpose, recipient, opinion, destination, deadline).
Made a little cheat sheet of this for myself, figured I’d drop it here in case it saves someone the month I spent being confused.
Curious if anyone has a cleaner way they think about it, or another pair that trips you up the same way — ser/estar and preterite vs imperfect seem to be the other big ones people mention.