To agree to the salesman's compromise is comfortable and easy. That's really why we do it. Those uncomfortable moments with the salesman aren't fun for most of us and we're looking to get out and get a deal we can brag to friends and family about.
Taking the second offer, with a couple of easy throw-ins from the company, makes us feel like we fought for our deal. Meanwhile, the company is collecting checks... usually from us.
Next time you need to negotiate, don't let fear and aversion to pain drive your negotiating process. Enter with a clear goal and negotiate with that in mind.
Find the creative solution, the weird solution, the one others don't think to ask because "there is just NO WAY it would ever work." Don't worry about being uncomfortable, embrace the moment, love the hardness, and work with the conflict moments to find the great deals around the edges and you'll walk away with better deals and far less remorse.