It was difficult to find a definition for ennui that did not merely reduce to 'boredom.' It is a state of nihilism. It is a sense of undefined purpose. It is lifting one's hands to the heaven and crying, "What is it all for?"
Ultimately, the best definition I could find was from the French Wikipedia page:
"Dans l’existence quotidienne, lorsqu'un individu est occupé par des activités, il sait bien que ce sont ses finalités qui lui donnent un sens, que ce soit dans sa direction vectorielle ou dans son contenu de signification. C’est dans cette quotidienneté que peut survenir un ennui mécanique, par ex. un ennui au sens de quelque chose qui viendrait interrompre une activité, qui viendrait en différer la continuité temporelle entraînant l'individu à s'occuper à autre chose."
The sense that, somehow, one ought to be something better than THIS.
Core to the problem of encouraging players to expand their 'characters' ... that is, to play the character as something larger than a composite of numbers, and to seek something greater than treasure and the next level. But if the game is ever going to be more than that, you cannot expect to stir players from their habitual play without giving them some sort of reward ... and where it comes to roleplay, more of the same reward - gold and x.p. - just isn't cutting it.
Maybe it is in your world. But I've made the argument before in my world; I don't increase a character's combat ability by giving x.p. for talking.
There are two ways to motivate behavior, and the first is very definitely the positive. Player doggy does good thing, player doggy gets treat. Very simple, very comprehensible, even to the dumbest of players. Of course, the treat has to be very good. It has to be so good, in fact, that it continues to be a treat long after it has been given again and again. And so treats work well for dogs. Dogs are very stupid. It doesn't occur to them that the treat today is the same treat yesterday.
People, however ... are a little tougher. But again, gold and x.p. are great treats, and for the most part fairly reliable throughout a long campaign.
The other motivation is the wonderful negative ... which no one likes, which we are told doesn't work, and that only the most sadistic of game designers would build into a game as something forced, irreconcilable and endlessly annoying. So naturally, every game designer does. Inevitably, your Sim is going to have to pee. Your ammo will run out. So will your hit points. One way or another, everything you possess, everything you love, everything that makes you a huge success at the game, will be worn down by old Father Time, in the way the old bastard does. At least, it will if the game is worth playing past the 80th hour.
This negative aspect to life is something that we are very familiar with in life, and therefore it is central to our sense of pleasure and activity. We're enjoying ourselves hard core in the here and now because they now is going fast and the here ain't going to be tomorrow morning at work. Therefore, drunkedness, howling at the moon, wild sex, six days in Fort Lauderdale and 62 hours at PAX is all that we have to make our lives as rich and meaningful as we're able.
If you want you players to see their characters have a reason to howl at the moon, you will have to incorporate something that will make them absolutely flippin' miserable in the in and between time. And with that in mind, I'd like to suggest - without any intention of incorporation in my own world - the implementation of Ennui.
Ennui is something that accumulated over time. It is something that is accumulated directly in relation to the collection of gold and x.p. Every time a character gets richer, gets wounded, comes near to death, travels with dreadful regularity upon the roads, seeing nothing but inns for weeks at a time, there's a little bit of Ennui that's added. A point here, a point there. Two points. Three points. Slowly, steadily moving towards a tipping point - one based upon intelligence and wisdom, naturally. The higher they are, the more quickly ennui approaches that inevitable number, the "tipping point," where life just ceases to matter.
The effects? Listlessness, obviously. A lack of focus. A reduction in strength, constitution and dexterity; lacking the will to avoid being hit, lacking the will to hit, for what does it matter anyway? You kill, you are killed, it's all part of one great nothingness. In fact, the sooner it happens, the sooner you'll be swept away from this ongoing, meaningless and exhausting existence ... "For the love of all that's decent, I hope the motherbastard rolls a 20 and ends my misery."
The cure? Occupation. Purpose. Novelty, but in the greater sense, nuance. The gathering of all ones resources applied to something more relevant than gold and x.p. Yes, yes, we can seek the tavern for a night of debauchery, that might lower the ennui a few points. We might seek the church, attend services, find greater meaning, that might lower the ennui a few more. Or perhaps a swift, clean kill in an alleyway, some meaningless but thoroughly enjoyable sadistic murder to fill one's spirit with a truly unique moment. Perhaps a session with a roped whip in one's private chambers ... a little asceticism is good for the soul. Or else, Festival! Oh, let's travel the two hundred miles to Land's End to see the Festival that begins in a month there ... wouldn't that be something? Lift our spirits, destroy a dozen points of ennui, refresh our appetites. Or perhaps a pilgrimage ... on foot, naturally, eschewing the horses and moving along day by day, as the GODS intended. When I am climbing the Thousand Stairs of Tuulaj's Sacrificial Altar on my bloody knees, then at last my ennui will be eliminated altogether.
There's only value if it takes a hundred hours of game play to accumulate enough ennui to matter; and only if it takes a hundred hours of game play to reduce it again to nothing. And one must remember - if the tavern worked last week, surely it won't satisfy the bill today. If the church is good for a few services, it too will simply fail to register. True, Festival is only once a year, but if we begin to attend them all, month by month, then again, what is it all for? It's just another everlasting road, another meaningless milestone that might as well hang about my neck for all the good its done me.
If I had any intention of following through, there would be two tables here ... one very short one for accumulation of ennui, and one very, very long one for getting rid of it. With kept notes for how long its been since something was tried, and how likely it would work if it were tried again too soon.
But surely, none of us would want to live under this sort of regime, would we? Let us keep our steady pace towards the next level, and let's not think too closely upon the vicissitudes of life. Contrast is such an enormous effort ... who needs it?