We cannot despair of humanity, since we ourselves are human beings.
Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.
In the midst of difficulty lies opportunity.
You can never solve a problem with the same kind of thinking that created the problem in the first place.
Only a very dull man spells a word the same way twice.
The formulation of the problem is often more essential than its solution, which may be merely a matter of mathematical or experimental skill.