It's a fantasy role-playing game.

DM: You are Vax Vax'ildan, a half-elf rogue . You are the member of the famous group of adventurers. Previously, Keyleth races around the corner and casts Sunbeam, aiming it at Sylas and Cassandra (and incidentally hitting Grog, who is caught between them). Cassandra manages an uncanny dodge but Sylas is caught by part of the beam, recoiling in horror as part of his face is burned to ash, exposing his vampiric fangs.
DM: Okay, so that ends Keyleth's turn. Back to the top, Delilah. Delilah is now going to step out of the cloud, which is now dissipating at this point.
Player: Is she taking a step away from me?
DM: Yes.
Player: I'm taking my blade with the poison on it, and I'm going to slash at her.
DM: Okay, as your reaction.
Player: That is an 18.
DM: 18 would hit her.
Player: Okay, that had whatever that poison is that I sold my soul to a hag for.
DM: Yes, it did. So roll damage on that.
