Myself vs by myself
"I did it by myself" and "I did it myself"; what's the exact and subtle difference between the two?
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The first means that the speaker did it alone, without any help. In the second, myself emphasises that the speaker did it, and no one else.
Literally "by myself" would mean "with myself", using a sense of by that we don't really have any more. This is illogical considered on its own, but if you think of it as an answer to the question "who was you with?" then it's easy enough to see how it would be sensible to say "I was with me" and not intend it to be taken literally. These days it would be a very well-known idiom to the point where we don't even think about how those two words come to that meaning, we just think of "by oneself" meaning oneself without company.