There is only one corner of the universe you can be certain of improving, and that's your own self. Aldous Huxley
Truth is no harlot who throws her arms round the neck of him who does not desire her; on the contrary, she is so coy a beauty that even the man who sacrifices everything to her can still not be certain of her favors. Arthur Schopenhauer
Write a paper promising salvation, make it a 'structured' something or a 'virtual' something, or 'abstract', 'distributed' or 'higher-order' or 'applicative' and you can almost be certain of having started a new cult. Edsger W. Dijkstra
It is one of the most saddening things in life that, try as we may, we can never be certain of making people happy, whereas we can almost always be certain of making them unhappy. Thomas Henry Huxley
It is difficult to be sure of our friends, but it is possible to be certain of our loyalty to them. John Lancaster Spalding
We can never be certain of our courage until we have faced danger. François de La Rochefoucauld