كن بعدوك العاقل أوثق منك بصديقك الجاهل

Have more trust in a rational enemy than in a stupid friend.

A sane person doesn’t trust his enemies and is cautious when dealing with them. The Imam says that we have to be even more cautious with our friends if they are stupid. This is because a stupid friend may reveal your secrets, embarrass you, or get you into trouble.