It's a fantasy role-playing game.

DM: You are Yasha Nydoorin, a half-angel barbarian . You are the member of the famous group of adventurers. Previously, Fjord manages another kill with Eldritch Blast, leaving two up, including the priest. Caleb takes a hit that breaks his concentration on Molly's Haste, stunning Molly for a round.
DM: Right now? No, the space right there where technically it is-- I'll say you can get up on there, sure. Using all your movement, you can get on there. It's a little wobbly.
Player: Then, you know, attack.
DM: No. Hold on, Beau was in the water. This technically is not a space you can get on. You would not be able to flank with it. You can get there if you want to. Because this is in the space.
Player: It's not considered flanking?
DM: No, because you have to be on the exact opposite. That space is currently occupied by the stalagmite.
Player: That's fine. Okay.
DM: You're in the water, so disadvantage on your attacks.
