What states the two main reasons why George didn't want Lennie to have a mouse in the first chapter of the Of Mice and Men?

The main two main reasons why George didn't want Lennie to have a mouse are that he kills the mouse without knowing/realizing his own strength when the mice bite him, and Lennie bothers George by bringing that same mouse but Lennie doesn't know that bothers him. Lennie acts like a child mental.