In one word

[BikerDude]

I hope this isn't overly exhausting..

Based on the movie, IN ONE WORD, what would you say was the Dude's motivation moment to moment? Include the definition of the word as you use it as his central motivation.
And what specific dialog in the movie supports the answer?

The screenplay is here.
http://bednark.com/big.lebowski.script.html

[Hominid]

Love? Concern? Zesty coitus?  I think that the search for a Lebowskian toe (theory of everything) is a journey left to the classically trained philosophers among us. (If there are any).

I say that because I see him having multiple catalysts for his actions: love, concern, greed for money... 

[milnie]

Bollocks!

[BikerDude]

Bollocks!

LMFAO!
Love it!

[Hominid]

OH! So we're just being facetious? In that case...


VAGINA!!!!!!!!!!!!!!!!!!!!!!!!

[BikerDude]

OH! So we're just being facetious? In that case...


VAGINA!!!!!!!!!!!!!!!!!!!!!!!!

Well facetious or not, that is the most common motivation for any Dude.
But actually I was posting this as a sort of exercise in Dudeist exploration.
A scene by scene analysis would be cool.
Of course I admit that I'd it very exhausting.

[Hominid]

We'd need incentive. Like free bowling for a night, or a few oat sodas. Or a day with Bunny... without nihilistic pool scum.