It's your character
As a player, you have a lot of creative control over what your character actually thinks and does. Several years of RPG experience have shown me that this can be a greatly effective tool. As a fellow gamer is fond of saying, you can paint almost anything.
Let me give you a few examples off the top of my head:
Maybe Asmodeus's plan to achieve godhood actually requires that he
be defeated twice over the span of 144 years. He was thwarted once,
in the past, by a party not too dissimilar to yours, and now it's
your turn. Sixty-eight years from now, that's when he'll finally
Maybe that's not actually true, but your character is convinced
that it is, because someone with high influence posing as another
worshiper of Asmodeus "let you in on the secret", and now you're
actually working against your patron, but your character has just
Or maybe, Asmodeus doesn't actually want godhood, but he needs to
take a convincing stab at it, as part of a power play to gain
influence over some other aspect. So he made sure there was a party
out there strong enough to "stop" him, and he also made sure one of
his trusted followers was in there, so that they actually succeed in
stopping him. Devious devil, that guy.
Or maybe it's something else entirely. The point is that, as a player, you need to work with the group, but that is (almost) never incompatible with whatever character framework you want to create. You just have to find the right character motivation that connects that framework to the group agenda.
But it's the table's story
Note that all of this is about how you the player view your own character. The actual fictional truth (so to speak) is largely under the GM's purview and is, in fact, subject to arbitrary change until it is narrated at the table. But even if that narration contradicts what you had imagined, in my experience, it still remains possible to reconcile the character's views with the actual fictional events without any fundamental change to his mental framework.
Naturally, you have nothing to lose in discussing all of this with your GM. It'll make that reconciliation (and his job of managing the flow of the story) that much easier.
I have tried this technique myself with great success. Many (most?) times, the motivations I decided internally ended up not clashing with the story at all. The few times that it did, we hashed it out at the table and the story became richer for it.
I have also seen it done by a few other players a few times, and I speculate that it's happened a lot more, but because it's simply a largely internal process, it simply didn't come up.
Once only, I had a player that was unable to reconcile. From what I gathered from the discussion, that was due to them being much too invested in all the minute details they cooked up in their head. That player was left with a dissatisfied feeling about the campaign and his character, and ended up quitting shortly thereafter, even though everyone was more than willing to accommodate them.
So I guess the caveat is, when you (re-)imagine your character's motivations, don't conjure up too much detail, or you may paint yourself into a corner if they happen to clash with the story at the table.