I wonder how the impersonal third-person subject affects the meaning of "non mi riesce di farlo", as opposed to saying "non riesco a farlo".
According to what it's explained in Treccani dictionary (see point 4 a from "Con sign. attenuato, essere capace"), there is no difference in meaning between these two constructions with the sense of "not being able to do something".– Charo ♦May 28, 2018 at 13:39
I think it's only a regional difference, because they have the same meaning.
However, "Non riesco a farlo" is more common both in written and spoken language than the other phrase.
2Welcome to Italian.SE! Can you precise what do you mean by a 'dialectal' difference? I think you mean that the frequency of the two expressions has regional variations, but I'm not 100% sure.– Denis Nardin ♦Jun 7, 2018 at 14:32
Yes, one phrase is more frequent than the other depending on the region. For example, in my area (I live in the center, Umbria) we say "Non ci riesco", that is another form but basically has the same meaning.– giacom0cJun 7, 2018 at 14:37
I took the liberty to edit to clarify. Please revert if you disagree with the edit.– Denis Nardin ♦Jun 7, 2018 at 14:39