Just learn a thing from videogames, and give them precise [Main Goals + Sub Goals + Optional Goals]
in order to [finish the game]
You can even make it meta, but at least them know what they must
ultimately do... How they get there is up to them.
(IMO 1/2 the things that stop players are having no idea what to do, 1/4 always looking for the perfect
solution instead of the viable
one, and 1/4 scare of failure/dying.
That might work with some players though not all. )
Otherwise, best rules in the universe won't work if 1) Nobody cares, and 2) Impossible to enforce in the first place.