It has been said that understanding a person completely leads one to forgive that person entirely.
Conclusion
You'll never be able to completely forgive yourself.
Evidence
You'll never be able to completely understand yourself, and understanding a person leads to completely forgiving that person.
Evaluate
This got pretty deep. Once you return from staring into the void of your own self-reflection, questioning whether you completely understand yourself and whether you'll ever [gulp] completely forgive yourself, we'll talk about the argument.
We are getting absolute language in this argument, so we might want to think about this conditionally. If we see conditional logic appear on a Flaw question, then we're going to see a Necessary vs. Sufficient flaw 9 out of 10 times (a backwards or opposite inference from a conditional rule).
The conclusion is saying that we'll never forgive ourselves.
Why? What's the rule for forgiving yourself? What do you need that we don't have?
The first sentence is the only time we talk about forgiving ourselves. There is conditional/causal language like "X leads to Y".
understand forgive person → person completely completely
The author then reasons
PREMISE → CONCLUSION Can't understand Can't forgive yourself fully. yourself fully.
That's an illegal opposite move, which goes by the name of Necessary vs. Sufficient.
Goal
Look for an answer describing the Necessary vs. Sufficient error, or one pointing out that even though we can't understand ourselves fully (which is one way to get complete forgiveness), there might be some other method we can use that also leads one to forgive themselves entirely.