If you think you understand it, that only shows that you don't know the first thing about it.

Those who are not shocked when they first come across quantum theory cannot possibly have understood it.

We depend on our words... Our task is to communicate experience and ideas to others. We must strive continually to extend the scope of our description, but in such a way that our messages do not thereby lose their objective or unambiguous character... We are suspended in language in such a way that we cannot say what is up and what is down. The word "reality" is also a word, a word which we must learn to use correctly.

Truth is something that we can attempt to doubt, and then perhaps, after much exertion, discover that part of the doubt is not justified.

Every sentence I utter must be understood not as an affirmation, but as a question.

No, no, you're not thinking; you're just being logical.

It is the hallmark of any deep truth that its negation is also a deep truth.