“Regard him as loyal, and you will make him loyal.”
Seneca suggests that suspicion can become self-reinforcing: treating a chosen friend as trustworthy helps create the conditions for candid, reciprocal friendship rather than teaching defensiveness from the outset.
Source note: Moral Letters to Lucilius, Letter 3, Richard M. Gummere translation. Seneca immediately contrasts this with people who fear deception so strongly that their suspicions help teach others to deceive them.