I don't understand what the sentence below say, please help me.
in and of itself
It is also put simply as in itself, as in: “This account may be true in itself.”
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The phrasing "in itself" is unusual, and is mostly used in a legal context. People who write legal documents often use complex language to make sure that the meaning cannot be misunderstood later.
In this case, there are two parts to this sentence to consider:
This account may be true...
In this case, the "account" means a story being told or reported by a person. For instance, someone might say "He claims he wasn't drinking, but his wife's account of the evening doesn't agree."
Whoever is speaking is saying that this story may be true. This means that it could be true, and also could be false.
[This account may be true] in itself.
The phrase "in itself" (as your dictionary link confirms) means to be self-contained. In this case, the author is saying that there is a chance this story is true, taken alone.
For instance: "He claims he wasn't drinking, but his wife's account says he kept getting beers from the refrigerator." "Well, he had a lot of guests, so perhaps he was getting beers for other people and not drinking them himself. Both stories could be true, in themselves."