The essence of knowledge is, having it, to apply it; not having it, to confess your ignorance.

Real knowledge is to know the extent of one's ignorance.

Some are born with knowledge, some derive it from study, and some acquire it only after a painful realization of their ignorance. But the knowledge being possessed, it comes to the same thing. Some study with a natural ease, some from a desire for advantages, and some by strenuous effort. But the achievement being made, it comes to the same thing.

Ignorance is the curse of God; knowledge is the wing wherewith we fly to heaven.

Ignorance more frequently begets confidence than does knowledge: it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science.

Beware of false knowledge; it is more dangerous than ignorance.