Il n'est pas certain que tout soit incertain.
(Translation: It is not certain that everything is uncertain.)

Whenever we proceed from the known into the unknown we may hope to understand, but we may have to learn at the same time a new meaning of the word 'understanding.

Translation: "What we know is not much. What we do not know is immense."

Still we say as we go,— "Strange to think by the way
Whatever there is to know, That shall we know one day."

We can never be quite clear whether we are referring to the world as it is or to the world as we see it.

It's difficult to explain. We're still very confused.

The fact that you are not sure means that it is possible that there is another way someday.

Whatever there is to know, That shall we know one day.

It might have meant something, or it might not have. That was the thing about uncertainty, you were never sure.

We don't know what the future will bring, but that's because we are ever in the process of creating it, not because it is an alien force to which we have to submit.

We don’t know what tomorrow brings, but we need to apply that.

We seem never to know what any thing means or is worth until we have lost it.

We do not know enough about how the present will lead into the future. We shall never be able to say, "Ha! My perception, my accounting for that series, will indeed cover its next and future components," or "Next time I meet with these phenomena, I shall be able to predict their total course.

We cannot know the mystery of the future.