“No” needs to be said before the roll, IMO. Then If the player insists on doing something impossible anyway, just role-play the failure. With that said, actions that are in a narrow sense impossible can still have positive outcomes and if there’s the potential for that then I’d say roll for it. The proverbial dragon seduction attempt can still possibly flatter a dragon with a big ego enough to benefit the PC even if it doesn’t get the PC laid.
“No” needs to be said before the roll, IMO. Then If the player insists on doing something impossible anyway, just role-play the failure. With that said, actions that are in a narrow sense impossible can still have positive outcomes and if there’s the potential for that then I’d say roll for it. The proverbial dragon seduction attempt can still possibly flatter a dragon with a big ego enough to benefit the PC even if it doesn’t get the PC laid.