There are many whose faults go undetected only because they are ineffectual
"There are many whose faults go undetected only because they are ineffectual: when these grow confident of their strength, they will act no less audaciously than those whose fortunes have already given them opportunity. They lack only the resources to display the full extent of their iniquity. Even a poisonous snake is safe to handle in cold weather, when it is sluggish. Its venom is still there, but inactive. In the same way, there are many people whose cruelty, ambition, or self-indulgence fails to match the most outrageous cases only by the grace of fortune. Just give them the power to do what they want, and you will see: they want the same things as others do."
- Seneca, Letters 42.3
This quote is highly relevant for the discussion of whether, say, Marcus Aurelius, Epictetus or Musonius were better human beings than Seneca. The simple answer is: we have no way of knowing and if anyone should be tempted to think that he or she knows enough about another person to judge whether that person is a good human being, he or she is almost certainly mistaken.
"He’s convinced you already, has he, that he is a good man? In point of fact, it is not possible for a good man either to come into being or to be recognized in such a short time."