If lag exists this creates a fair - but really unfair feeling game. Clients will constantly be reporting shots at enemies that were quite accurate when the shot was taken but are now extremely off the mark.
As the article mentions - fully server authoritativeness works great in lan situations and for single player content but can really fall on its face in multiplayer.
If I, as a user, am constantly moving in random directions and have a lower ping than you (and thus my movements are reported to the server before you can actually observe them on your machine) then you should never hit me except through pure blind luck - in fact accurate shots could be the only shots that are guaranteed not to hit.
Games want to feel bad at a range of reasonable pings - and reasonable pings usually stretch into the range of 100 or 150 ms - that leads to up to a half a second of lag between when I dodge left and you, as a shooter, would have the earliest chance to actually register a shot with the server at my new position.
Additionally, the server can reconstruct what it thinks we saw at a given moment in time - but the server doesn't know what data has been lost[1] and whether the client might think it was right - or even whether the client might be misreporting dropped packets to engineer an advantageous game state. Also, this whole time we've been discussing latency as if it's a fixed number - but it is constantly changing and the reporting of the latency is something you need to trust to a client since clients can always artificially inflate latency figures.
Due to lag correction either you're able to shoot me after I duck behind cover, or you're never able to shoot me - and both options suck for one half of the players involved.
1. See the two generals problem - proof of delivery is actually a hard problem.
As the article mentions - fully server authoritativeness works great in lan situations and for single player content but can really fall on its face in multiplayer.
If I, as a user, am constantly moving in random directions and have a lower ping than you (and thus my movements are reported to the server before you can actually observe them on your machine) then you should never hit me except through pure blind luck - in fact accurate shots could be the only shots that are guaranteed not to hit.
Games want to feel bad at a range of reasonable pings - and reasonable pings usually stretch into the range of 100 or 150 ms - that leads to up to a half a second of lag between when I dodge left and you, as a shooter, would have the earliest chance to actually register a shot with the server at my new position.
Additionally, the server can reconstruct what it thinks we saw at a given moment in time - but the server doesn't know what data has been lost[1] and whether the client might think it was right - or even whether the client might be misreporting dropped packets to engineer an advantageous game state. Also, this whole time we've been discussing latency as if it's a fixed number - but it is constantly changing and the reporting of the latency is something you need to trust to a client since clients can always artificially inflate latency figures.
Due to lag correction either you're able to shoot me after I duck behind cover, or you're never able to shoot me - and both options suck for one half of the players involved.
1. See the two generals problem - proof of delivery is actually a hard problem.