It's a fantasy role-playing game.

DM: You are Grog Strongjaw, a goliath barbarian . You are the member of the famous group of adventurers. Previously, The undead dragon -- none other than the slain white dragon, Obatalá, that once served as Arkhan's mount -- unleashes a breath of bone shards at him. Vox Machina leap to Arkhan's defense, deciding it is best to face the Briarwoods now rather than later.
DM: That's easy enough. Make an athletics check, actually, in case something goes horribly bad. You are raging, so you get advantage.
Player: 25.
DM: Okay. Easy enough. At that height, you take eight points of bludgeoning damage, reduced to four, and (impact) you land, arcing over her, both feet to each side of her, and you're standing, looming over her body as she's wrapped up in vines, going (grunting).
Player: I fucking hate this dead bitch. And I raise the sword and start swinging down in these huge arcs at her. The first two attacks at her.
DM: Okay. As you pull the blade up, the voice goes, "Yes. Her. She's part of the web. Her. Her!" And you give into the fury. Go ahead and make your attacks.
Player: Are they with advantage because she's prone?
DM: Correct. Well, she's restrained.
