No insight isn’t really like that. It’s not an anti-persuasion. In my opinion, the DM can’t tell the player what to do, they can tell them what’s possible and they can bend the world to make one choice better than another but a good DM will make players feel like they have agency.

How insight works: Dm (lying in character): “oh it’s totally safe, you can trust me, this is the only way” Player: “can I roll insight to see if he’s lying?” DM: “sure” Player: “An eight” DM: “you can’t be sure”

Or

Player: Nat 20 DM: “He’s absolutely lying but the city guard is chasing you and you certainly won’t be safe with them either. You’re not sure exactly what part of what he said you can’t trust and you can’t tell the party without him overhearing. So are you going to keep it to yourself?”

It’s likely the same result that the story continues and they follow the guy but now it’s contextualized differently.