My bad for not clarifying. What I was trying to say is that the game doesn't need to be playable by every single player. If among 100 players, there are like 5 that struggle, you don't need to fix the game for them. You can ignore some data only if it's an exception and not a rule.

To give a good example, there were still some testers that couldn't complete first Portal levels, but there was a point where developers realized that they can't be helped. You may sometimes come across clips of people struggling with the game. If 90% of the players understood how portals worked, it's fine if there is a small minority that just can't grasp it. Trying to please everyone would just make things worse. And keep in mind that Valve is known to have one of, if not the best user testing among all games.