In one post, a commenter maintained that the phrases "I did my best" and "I did the best I could" don't mean quite the same thing.
To avoid starting a chat with a member whose profile page doesn't show that English is his mother tongue, I have to ask native English speakers:
Provided that "do one's best" is an idiom, is "I did the best I could" a proper phrase to be used at all?
If it is, is there really a fine difference between the two? If there is, what is it?