Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. Albert Einstein
In avoiding the appearance of evil, I am not sure but I have sometimes unnecessarily deprived myself and others of innocent enjoyments. Rutherford B. Hayes
Deliver me from writers who say the way they live doesn't matter. I'm not sure a bad person can write a good book, If art doesn't make us better, then what on earth is it for. Alice Walker
Since thou are not sure of a minute, throw not away an hour. Benjamin Franklin
You have cast away your own for that which you are not sure of. Xhosa Proverb
Who is not satisfied with himself will grow; who is not sure of his own correctness will learn many things. Chinese Proverb