Twilight, Rarity and Rainbow Dash meet a young pony who is angry at her brother's disinterest in life and his potential of being a great actor.
When confronting the brother pony, it is discovered that he has far too much pride in his own decisions and desires that makes it extremely difficult to convince him to change, and causes bigger rifts with his sister.
LESSONS:
1: Sometimes there's more than ONE WAY to get what you want. Even the MOST COMMON way is not the only way.
2: Give someone a fair chance REGARDLESS of their lack of experience or references. They may just surprise you.
3: You cannot change how somebody feels what is Right or Wrong, nor can you force them to believe in what you believe. All you can do is hope to set an example.