Plutarch De capienda ex inimicis utilitate 11

[11] But if our enemies arrive at high places in the courts of princes by flattery or frauds, by bribery or gifts, we should not be troubled at it, but should rather be pleased in comparing our undisguised and honest way of living with theirs which is quite contrary. For Plato, who was a competent judge, was of opinion that virtue was a more valuable treasure than all the riches above the earth or all the mines beneath it. And we ought’ evermore to have in readiness this saying of Solon: ¹ But we will not give up our virtue in exchange for their wealth. So will we never give up our virtue for the applause of crowded theatres, which may be won by a feast, nor for the loftiest seats among eunuchs, concubines, and royal satraps. For nothing that is worth any one’s appetite, nothing that is handsome or becoming a man, can proceed from that which is in itself evil and base. But, as Plato repeats once and again, the lover cannot see the faults of the thing or person that he loves, and we apprehend soonest what our enemies do amiss; therefore we must let neither our joy at their miscarriages nor our sorrow at their successes be idle and useless to ourselves, but we are bound to consider in both respects, how we may render ourselves better than they are, by avoiding what is faulty and vicious in them, and how we may not prove worse than they, if we imitate them in what they do excel.