Mental processes are means to ends in the struggle for existence.

I don't want to be a teacher. I want to be a friend.

领导力意味着为了更美好的明天而在今天做出艰难的决定。

Mathematics is not a deductive science—that's a cliché. When you try to prove a theorem, you don't just list the hypotheses and then start to reason. What you do is trial and error, experimentation, guesswork.