Failures in human attempts
The LORD knoweth the thoughts of man, that they are vanity. Ps 94:11
What about evil?
Failure in understanding good leads to failure in understanding evil. In guiding individuals to form their lives around self-realization humanism directs them straight to destruction. It is in defending one's ego, interests and possibilities that humans are ready to cause most evil outcomes and neglegt people in most severe ways. That is an everyday reality with everyday destructive results and misery. But even so, humanism can't form it into a simple ethical statement that egoism is evil.
The magnitude of failure is then easy to see. Good is defined in a waywhich directs attention to self. Evil on the other hand is something humanism wants to forget altogether. It is left without addressing.