WARNING: This article contains major spoilers for Supernatural season 15 episode 10. Read at your own risk.
Supernatural season 15 episode 10 aired last Thursday night on the CW, with the title "The Heroes' Journey." The episode sees Sam and Dean going on a trip to help an old friend. However, it looks like they've been finally out of luck, and they're now the ones who need help.
Sam and Dean's life have never been easy, but in Supernatural season 15 episode 10, their day is just like a normal bad day -- like what other people experience. The episode still featured supernatural weirdness, but the story focused mostly on normal people stuff.
In Supernatural season 15, episode 10, Dean felt he has no control over his life and said he and Sam were experiencing a "super normal day." Perhaps, the best part of his day was when he learned Garth named his twins Cas and Sam, though he thought he had more influence on Garth.
Despite the strangeness of their day, God reprieved Sam and Dean. However, they know things will get ugly sooner than later. Cas is in heaven to search for some information about Chuck, so both of them didn't have anything to do. That's why they visited Garth in Supernatural season 15 episode 10.
Garth explained to Sam and Dean what he thought was Chuck was doing. He also suspected that the two brothers didn't know how to deal with normal. Sam wanted to fix it, but Chuck's story couldn't be changed. Yet, the point of them having a normal bad day is to show how their lives would be if they're normal.
If they realized being normal isn't that bad, then they could live a normal life and not have to deal with supernatural weirdness. Later on, they found out that even though Chuck was the one writing their story, their blood and guts help them survive and get through everything.
Their realization is helpful in the future since they knew they're capable of everything. Although viewers knew that, it took a normal bad day for Sam and Dean to see it as well. It looks like Chuck reverted to being a good God and showed the brothers the different parts of themselves.
Possibly, Chuck doesn't want to write the ending of Sam and Dean since he wants them to do it. He said previously that no matter what he writes, their ending is all the same. Perhaps, he meant that he couldn't write the brothers' ending since they have to write the ending themselves.
