How cautious we must always be when faced with those who, far beyond observing deeds, can gaze in wisdom on our very thoughts.

Ah, how cautiously a man should breathe
near those who see not only what we do,
but have the sense which reads the mind beneath

One must take care with those who have the wit
Not only to observe the action, but see
The thought as well!

They were admirable things for the observer - excellent for drawing the veil from men's motives and actions. But for the trained reasoner to admit such intrusions into his own delicate and finely adjusted temperament was to introduce a distracting factor which might throw a doubt upon all his mental results. Grit in a sensitive instrument, or a crack in one of his own high-power lenses, would not be more disturbing than a strong emotion in a nature such as his.

How prone to doubt, how cautious are the wise!

It is the thoughts of men that are deceitful, Their pledges that are loose.

No one would have believed in the last years of the nineteenth century that this world was being watched keenly and closely by intelligences greater than man's and yet as mortal as his own; that as men busied themselves about their various concerns they were scrutinised and studied, perhaps almost as narrowly as a man with a microscope might scrutinise the transient creatures that swarm and multiply in a drop of water.

Other men are lenses through which we read our own minds.

men’s actions are the best guides to their thoughts

Knowledge dwells in heads replete with thoughts of other men; wisdom in minds attentive to their own.

Mark this well, you proud men of action: You are nothing but the unwitting agents of the men of thought who often, in quiet self-effacement, mark out most exactly all your doings in advance.

There be many wise men, that have secret hearts, and transparent countenances.

Observers trying to decide what a man is like look closely at his actions.

When people think the world of you, be careful with them.