People often forget perspective and attack angles and blame Lag Comp for their ignorance. There is a reason Soldiers and Law Enforcement Officers move tactically and approach corners from angles, some call it Slicing the Pie.
A lot of people on this game go charging around corners, and an opponent out of their line of sight kills them as a result... then blame it on lag.
Sometimes people just have a tactical or visual advantage on you and thus "get the drop on you"/