Frank J. Wilstach, comp. A Dictionary of Similes. 1916.

Reason

Reasons are like liquors, and there are some of such nature as none but strong heads can bear.
—Edmund Burke

Reason is to faith as the eye is to the telescope.
—John Caird

Reason, like virtue, in a medium lies:
A hair-breadth more might make us mad, not wise.
—Walter Harte

Human reason is like a drunken man on horseback; set it up on one side, and it tumbles over on the other.
—Martin Luther