Understanding 自分は in this sentence (and other potential gross misunderstandings) > > He put the receiver down and, while stroking his moustache, Mr Dursely thought. > ------ **** > _I'm being stupid_ I'm really stuck on the line in bold. So I guess I can translate as "really". I think it intensifies the rest of the sentence. Is this right? I think in this case is "how..." so would be "Really! How stupid I am!" So, if what I've got so far isn't gibberish, I don't know how to fit in the part. Literally I suppose it would be "Really! As for myself, how stupid I am!". But, is really necessary? Why? How should I think about it?

Translating this as "Really!" is not wrong, but may be a bit too weak. I feel it's closer to "That can't be!", "Unbelievable!", "I never dreamed of it!", etc. It's not an intensifier but an interjection-like expression on its own. That is, it's not directly connected to the remaining part of the sentence.

is necessary in this case. This is because works as a comment about the surprising news he just heard. Without that explicitly switches the topic, the last half of the sentence would mean "How stupid it/he/she is!", referring to the news. Compare:

> !
> Unbelievable! How stupid! (←this refers to the news itself)
>
> !
> Unbelievable! How stupid I am! (←he is disappointed at himself because he could not think of the possibility of what he heard)