Doubt is the abettor of tyranny.

Doubt is important to knowledge — He knows not how to know who knows not also how to unknow.

Doubt is important to faith — A faith which does not doubt is a dead faith.

Doubt is healthy — Human beings are perhaps never more frightening than when they are convinced beyond doubt that they are right.

Fatigue makes women talk more and men less.

Fatigue is like an unwelcome in-law: If you keep quiet, smile, and hang tough, eventually it will leave.

Fatigue is the best pillow.

Fatigue is the condition of a philosopher after having considered human wisdom and virtue.

Fear is the fire that melts Icarian wings.

Fear is many-eyed.

Fear is the parent of cruelty.

Fear is the mother of superstition.