I hate it when he is lazy: What does 'it' refer to?

English as a Second Language English Vocabulary, Grammar and Idioms
1

Dear teachers,

Please read:

I hate it when he is lazy.

What does “it” refer to?
This structure is strange for me. Do you know the rule?

Thanks
Quoc

2

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This is just an introductory-it in the middle of a sentence. It serves the same purpose: to postpone another sentence element (here, when he is lazy) to a position of greater emphasis.
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