Single-file lines. The world teaches us to stand in them, almost without thinking about it. Counter-Strike proposes an alternative: you really, really should just never do that.
Counter-Strike player ggHushHush posted a highlight in which they took a Scout sniper shot at what appeared to be one enemy player emerging from a smoke grenade haze. It turned out to be four, three of which were right behind the first.
As you can see, the bullet sailed through them all with ease, like a bowling ball in an alley made of bumpers. Crazy. (I also really enjoy the other guy who runs in all like, "Alright lowly teamfriend thanks for taking point I guess, now time for me to save the day with MY GRENADE YEAAAAAH.")
For players, though, there's also some useful information in here. The Scout packs more punch than many think, but only under certain conditions. As one player explained, if you want to one-shot somebody with a Scout like this, you've got to go for the gut (not the chest), and your enemies can't be wearing kevlar.
So, in summary: Scout surprisingly good, straight lines very bad. The more you know.