The first Assassin's Creed game only had side missions because "the CEO's kid played it".
That's the start of the wild story behind the addition of side missions to the 2007 game, as told by then Ubisoft fight system AI lead Charles Randall in a fascinating Twitter thread.
The first Assassin's Creed contains a number of flag collecting missions, as well as Templar assassinations. These "additional memories" do not advance the plot.
It turns out Assassin's Creed was ready to ship without these side missions when, just days before the game had to be sent to shops, "the CEO's kid played the game and said it was boring and there was nothing to do in the game".
Randall and a handful of others added the side missions in the main conference building of Montreal's Peck Building, a former textile factory where Ubisoft Montreal was founded. Randall explained this strike team managed to pull off the impossible: side missions in five days, but one bug slipped through the net.
This bug meant that sometimes you could never complete all of the Templar assassinations in order to get the full 1000 gamerscore on offer. This particular templar could fall through the world and despawn if approached from the wrong direction. The game considered him dead, but wouldn't credit the player for the kill. No more spawning meant players would have to start over.
This five day blast to add side content to Assassin's Creed sounds nightmarish, and Randall says he doesn't remember what happened in that period. "But I know it's a miracle that the game didn't just melt your console or whatever."
Assassin's Creed kickstarted one of the most popular video game franchises of the last and current generation, but the first game in the series had its problems. Its collectible system, which included the flag collecting, was roundly criticised as frustrating filler.
Now we know why it's in the game in the first place.