Random idea...
As has been said, before, for starters, power is an important motivator. I would imagine that the higher you get, the more dangerous it becomes. One, you need to get knowledge that is more difficult to obtain, and two, increasingly powerful characters will be wanting access to the information you have.
But, here's something better I think, patched together from the varius random stuff I've read tonight:
Your very studious Elven archvist falls madly in love. He meets his better half in Sigil, they hit it off, and seeing how Sigil is both the home of said better half and the nexus of multiversal traffic, he decides to move there. He leads a passional, happy, truly rewarding life, as would any character who spends all his time doing what he loves (in this case, let's say amassing knowledge and magical might) and who also has a wonderful personal life. No, even better than that, he leads the kind of life of which the qualities are ineffable, and which can only really be understood by those who have shared in something of the kind.
Until, that is, several years later. The love of his life dies. Nay, not dies, is destroyed, effectively removed from existence. Irrevocably. In Sigil. The cause of this (offended Her Serenity, killed by a factol, angered a draco-lich, taunted Coaxmetal a bit too far, etc.) is important only insofar as it makes it impossible for this very intelligent, learned man to bring her (let's say it's a woman, for the sake of argument) back. She is lost to him. He cannot even cast a "converse with dead" spell, to say a goodbye of some sort.
Now, here comes the turning point. Your character is quite intelligent, hard-working, high-level, and most importantly, driven forward with mad desire. He wants her back. He desperately, resolutely and uncompromisingly wants to get her back. There will be no tomfoolery of the "life-goes-on" sort, no quiet resignation to his fate, no philosophies of "what's done is done, be glad for what you had". Being an archivist, knowing full well the power of knowledge, drives you even further. You will get her back.
And here, the question lies: how? She cannot be resurrected. Her body is not available. Her spirit (if you choose to use such concepts in your game) is nowhere to be found. Casting Wish spells is of no effect. Your character cannot intercede with any power, but even if he could, it would not matter, as the last place in existence where his love was seen was the City of Doors. Your character is quite steeped in ancient and obscure lore already, and knows of Chronomancy and its associated possibilities. Alas, the Lady blocks time travel within the city, and casting any spell from this school is likely to draw her unneeded attention.
So, here is where you are. You know what you want, you have awesome power at your fingertips, and absolutely no clues on where to go next. Many, many interesting epic-level avenues are now open to you. Indeed, seeing how at this time your own life seems a concern about as important as the weather tomorrow, more avenues than before. Whither ?
Hope it helps.
Tal Rasha
