Dan Gallagher might have never met Alex if his friend Jimmy (Stuart Pankin) didn't make a fool of himself at the party. Jimmy tried to come on to Alex even though he was obviously married, and his wife was present. If this never happened, Dan would have just stayed with his wife the entire time, and leave without talking to Alex. Well of course, then there would be no plot and no movie!
Haha good point! Mind you he still would have met her (Alex), at the meeting the following morning and I suppose they could still have got chatting at the bar the night before even if Jimmy hadn't pointed Alex out in his foolish approach. I guess Alex would still have made the comment about Dan's umbrella "Was it made in Taiwan?" after said meeting and things could have still gone the same way.
That said, Alex knew Dan was married as a result of that party and this seemed to set up the whole challenge. She seemed to like the thrill of trying to break up his marriage as if to prove something to herself.
Funny how Jimmy then shook his head in disbelief when finally Dan confessed it all to him when HE was the one who first made a play for her (of sorts)!!
"These days you have to boil someone before you can sleep with them"