Do not compromise yourself or your beliefs in order to please other people or fit in with a system. Know who you are. Let other people know what you stand for. Do not give in to pressure to conform or to do things you do not agree with.
This may be used to explain the behavior of a person who is overly cautious about something. The wise person makes mistakes but does not usually make the same mistake twice.
I refuse to admit defeat yet. Though right now it looks like I may fall, there is still time for things to change. (The "fat lady" is an insulting reference to an opera soloist, opera often end with a female solo.)
Looking out for one's own personal welfare more than anything else. This is sometimes used to criticize a person who has abused or taken advantage of someone else, "All he was doing was looking out for number one." Or it may be used to defend himself or herself, "There is nothing wrong with what I did. I was just looking out for number one."