Does anyone know, what triggers the uncancellable "Go Out" action on sims, and if there are ways to prevent it from happening?

You invite someone over, and you are about to get "better aquainted" with them, they suddenly jump out of the bed, and run out...
Usually they don't even go home, and you can call them back in, only to get them running out again.

When that action starts appearing, the only way to get them finish what I meant them to do is building a fence next to the bed, so they cannot escape their "destiny", but I wish there was some other way.

Usually this happens if they have something to do, for example a job or a role (bartender etc.), or perhaps if they have low motives and return home to replenish them.

If the sim is an NPC who doesn't have a home in the town then they leave to return off-world.

That I would understand, but I have set everyones motives static, and they usually still stay on the lot.

I think it's there way to say "hey.. i don't wanto do this"

On serious note though:
Only a mod that can change npc's motives might work, using testingcheats to set static will only affect your household i belive.