Italian question: When do you use riuscire a vs. potere to say I can't do something?

Question

Italian question: When do you use riuscire a vs. potere to say I can't do something?

Answer 1

If you mean "I don't know how to" then it's "non so": "I can't swim" = "Non so nuotare" (the verb is "sapere") because you never learned how to swim.

If you mean "Something prevent me to do something" then "non posso": if you just had lunch, then you can't swim not because you don't know how to but because it's considered dangerous for your health: "I can't swim, now" here is "Non posso nuotare, adesso".

"Riuscire" means "manage to": "Non riuscivo a nuotare!" means "I was trying to swim, but I wasn't able to!"

Answer 2

Riuscire = I'm not able to...

Potere = I cannot do it....