But passive insight presents a host of problems for me. It sets that baseline number which a character can't roll below, of course. And that presents role-playing and story-telling problems. If a character has a high passive insight, then is the DM supposed to reveal all the plot secrets, and say things like: "Edgar the merchant comes to you and tells you that his daughter has been kidnapped, but Bob, your character has a high passive insight, so you think he might be lying to you." With a passive insight, it creates a situation where some players just know all the easy secrets and answers automatically. It prevents the ability of the DM to create mysteries, or problems that the PCs have to solve or work through if one character always has a good hunch about what's going on. And when "Bob" gets told that his character has a hunch about something, all the other players know that's correct information, which makes it difficult to play their characters as though they came to other conclusions.
Sometimes a PC's hunch is just way off, and I prefer to have them roll an insight checks whenever they want, where they might roll low. This is also one of the few rolls I will make behind the screen, so that when one or multiple characters ask to know if an NPC is trustworthy or lying, different characters may get told different things depending on their secret roll, and they simply must role-play their character based on the hunch they each get, because they don't really know how the roll went. It causes the group to perhaps rely on the one character who is very wise (has a high insight modifier) and is often able to suss out a situation correctly. But sometimes even that player gets things wrong.
