The more closely you look at one thing, the less closely can you see something else.

The solution of the difficulty is that the two mental pictures which experiment lead us to form - the one of the particles, the other of the waves - are both incomplete and have only the validity of analogies which are accurate only in limiting cases.

[T]he atoms or elementary particles themselves are not real; they form a world of potentialities or possibilities rather than one of things or facts.

In my paper the fact the XY was not equal to YX was very disagreeable to me. I felt this was the only point of difficulty in the whole scheme...and I was not able to solve it.

There are things that are so serious that you can only joke about them.

It seems sensible to discard all hope of observing hitherto unobservable quantities, such as the position and period of the electron... Instead it seems more reasonable to try to establish a theoretical quantum mechanics, analogous to classical mechanics, but in which only relations between observable quantities occur.

A consistent pursuit of classical physics forces a transformation in the very heart of that physics.