Many people do not understand themselves, nor do they try to gain self-understanding.
Conclusion (It is clear from this)
Anyone who lacks self-understanding will be incapable of understanding others.
Evidence
Many people don't understand themselves, nor do they try to gain self-understanding.
They might try to understand others, but this won't work, because without self-understanding it's impossible to understand others.
Evaluate
Whenever we see conditional logic show up on Flaw (in this case, anyone / incapable / sure to fail / without are all conditional indicator words), we should immediately start anticipating this is going to be a Necessary vs. Sufficient flaw, which means that the author presents a conditional logic premise but then uses that conditional rule in an illegal backwards or negated fashion in order to reach their conclusion.
We have a premise that says "without X, it is impossible to have Y". In other words, "X requires Y". ~self-understanding → ~understand others understand others → self-understanding
The conclusion actually says the exact same thing: If you lack self-understanding, you'll be incapable of understanding others. ~self-understanding → ~understand others
What does it mean if the conclusion just replicates a premise?
It is the mythic beast known as Circular Reasoning. Circular reasoning is one of the ten famous flaws, but it's primarily famous as a wrong answer choice. We see it offered all the time in answer choices (the conclusion restates a premise / the evidence presumes the truth of the conclusion), but it's almost never the real problem.
Goal
This is like seeing a leprechaun underneath a double-rainbow. A rare sight. Let's look for an answer describing the Circular reasoning that "one of the premises literally is the conclusion".