The spoilers at the end of a manhwa can be all kinds of things. Maybe a character's fate changes dramatically, or a long-hidden secret is revealed. But without knowing the specific manhwa, it's hard to give exact details.
A boy who always told lies could end up being alone and facing consequences like getting punished or having no one to rely on when he needed help. His lies would catch up with him eventually.
This could be a tale that shows the boy's struggle to break free from the pattern of lying and regain the trust of those around him. It might also explore the reasons behind his dishonesty.
It's often a combination of cultural influences and artistic innovation. Manhwa art styles can draw from traditional Korean aesthetics while also incorporating modern trends to create a unique look.