The "3 Episode" Rule in Anime
In book reading, there is a rule where you need to read atleast 50 page of a book and if it fails to impress you, return it to library. In anime, there is a similar rule and it is all decided by the first 3 episodes. Every people has different tastes in anime that they watch. If you like the show you continue and if not you dropped it. And this 3 episode rule will decide everything. A good story in anime must catch the viewer's attention at the first episode, particularly atleast the first 3 episode. Here's some example of anime that from the first episode itself, you can already say that this series is a masterpiece.
The Promised Neverland
Attach on Titan
Steins;Gate
Code Geass
Kanata no Astra
Made in Abyss
And many more
This anime managed to get viewer's curiosity and interest from just the very first episode itself. That must be the factors that most anime needs to have in the beginning of their stories. The quote "Save the best for last." shouldn't be applied in anime if you want your work to succeed. You have to put your best not just in first or last, but to every episode. That's what makes an anime "Masterpiece".
And I Can Only See 2 Purpose For This Rule
To save time. Why force yourself to finish an anime that aren't compelling. Watching anime is a time killer and you don't want to waste your time watching wastes. Just drop the show and find something to watch that suits your tastes more. It is better to waste 60 minutes worth of 3 episode than to torture your self into hours worth of episode in anime that failed to entertain their audience.
To challenge the writers/aspiring writers. This rule plays a big role in the decision if your story is good or not. Your story must have a strong foundation in order to build your story into a higher place. Just like building a tower, if your foundation is weak your tower might collapse. I've seen several anime with a story like this. It's either bland story all throughout the series or the first half of the story is bad and the last part is good. But what's the point of having a good ending if people stop watching your show because you failed the first part. "If you failed the 3 episode rule, you failed your self as a writer".
I know that I feel bad for the all the staffs behind the anime that I dropped. But it can't be help. I won't waste my time watching a show with weak impression. Just like I said, we have different tastes maybe there are some might like that anime and there are some that aren't. So if you watch an anime give it a chance of 3 episode then you decide whether you continue or drop.