Question

why I do something when I saw my friend stole a book from the library

Answer 1

If you really care your friend then you must complain about it so that he/she could not do so again such a bad thing. Yes at first he/she gets angry upon you, but time by time he will realise his/her mistake and will thanks you .

And you will able to put an example of good friendship for others.

please mark it as brainlist. Thankyou

Answer 2

You really care about your friend. You should either convince him not to steal the book or You should complain about him/her to the librarian so that he does not repeat it. It will be very kind act from you.