Seneca's Letters from a Stoic

Regard him as loyal, and you will make him loyal.

Some men shrink into dark corners, to such a degree that they see darkly by day."

It is equally faulty to trust everyone and to trust no one.

by their suspicions they have given their friend the right to do wrong.

fearing to be deceived, have taught men to deceive

Ponder for a long time whether you shall admit a given person to your friendship; but when you have decided to admit him, welcome him with all your heart and soul. Speak as boldly with him as with yourself

judge a man after they have made him their friend, instead of making him their friend after they have judged him.

When friendship is settled, you must trust; before friendship is formed, you must pass judgment.

you have in the same letter affirmed and denied that he is your friend.

But if you consider any man a friend whom you do not trust as you trust yourself, you are mightily mistaken and you do not sufficiently understand what true friendship means.