The difference lies within ourselves and how much we want to change for the better.

self-improvement normally leads to:

• failing your aims
• fake expectations
• fake aims
• mental disorders based on first 3 outcomes

I haven't seen people changing unless they accept them to be who they are.
Main thing in self-improvement - find peace with yourself and this will lead to happiness. And watching the world through happy eyes - makes the world aroung you to be a better place to live in.