One of the more well-known jokes among video game fans is that Valve doesn’t know how to count to the number three. There will likely never be a Half-Life 3, and the Half-Life 2 episodes stopped at two. But thanks to a new documentary, we have a reason why we never got Half-Life 2: Episode 3.

In the Half-Life 2: 20th Anniversary Documentary, posted on YouTube last week, former and current Valve developers break down the history of the now classic shooter. The philosophy behind the episodes, which followed the main game, was to “do more with less.” So Episode 1 had Alyx follow you throughout the game as an active companion, and players encountered the Hunters for the first time in Episode 2.

Technology was still at the heart of the episodes, and was looking really ambitious in terms of features. Developers interviewed for the documentary said they had some concepts for the final part, like how it would be set in the Arctic with a new ice gun that would let you create shapes like ice walls and ledges, and were around six months into development. But because of all the features, it would need a few more years before it could release.

Then Left 4 Dead became the priority. Valve dropped Episode 3 to work on it, but by the time it was done, the developers felt it was too late to go back. Valve engineer David Speyrer said it was “tragic and almost comical” that it “took long enough that then by the time we considering going back to Episode 3, the argument was made, like, “Well, we missed it. It’s too late now.”

There were also discussions that the team would need a new engine for the final episode, although Spreyer said that was “so wrong” in hindsight. Valve founder Gabe Newell said that just moving the story forward wasn’t enough.

“Yes, of course they love the story; they love many, many aspects of it. But sort of saying that your reason to do it is because people want to know what happens next … we could’ve shipped it, it wouldn’t have been that hard. My personal failure was being stumped. I couldn’t figure out why doing Episode 3 was pushing anything forward.”

Plus, the relatively small development team was interested in other technologies. Eventually this would lead to Half-Life: Alyx, the VR-exclusive spinoff.

There were other fun tidbits from the documentary on some fan-favorite elements of the game, and how it all came about. Here’s a partial list.