In the novel That was Then This is now, Bryon knows what's right from wrong while Mark doesn't. One example of this is when Bryon discovers that Mark has been dealing drugs and feels conflicted about keeping his secret, knowing that it is morally wrong.
A clear example in the novel That was Then This is now of Bryon knowing right from wrong while Mark doesn't comes in the scene where Bryon discovers that Mark has been dealing drugs.
Bryon is aware that selling drugs is morally wrong and dangerous, and he feels conflicted about keeping Mark's secret.
However, Mark doesn't appear to have the same understanding of the consequences of his actions. This example showcases Bryon's moral compass and his ability to differentiate between right and wrong.