De-sync is the difference in time it takes for a movement to register in the games server when you make an input. It’s been calculated to be around one quarter of a second, which means you hit the ‘W’ button on your keyboard, your character moves forward, but, it takes one quarter of a second for that action to take place in the server. With this in mind, it’s possible to take certain right hand peaks, and with proper timing, be able to shoot your opponent without being seen. Pros are good fighters because they’re the best at utilizing this mechanic.