tl;dr: "git gud" means less now than 2 months ago
The "Infallible" achievement is against the game's design. As time goes on, changes in the game have made it go from hard to almost impossible, e.g:
- Levels being more chaotic/random: Variations have been added that make it so you can't go auto-pilot all the time, and more are incoming (see today's trailer)
- In Door Dash they removed being able to distinct the correct one in the last three doors so it is 100% random and there is no incentive to go ahead
- Many casual players left the game and SBMM is not active right now: This means you can easily get people in your lobby much more skilled
- Many people got the achievement through the "quit before elimination screen" method and it has/will be patched
Sure you can still technically get the achievement with an incredible combination of skill and luck. My complaint is that the threshold gets higher every day, and the best moment for the achievement was early Season 1. While I definitely appreciate many of the changes to the levels, this achievement is aging badly and punishes you for not getting it before.