Wow this video is gold. This guy studies how decisions we make that seem rational really are not. Although this video wasn't directed toward affiliate marketing, advertising, increasing opt ins, or conversions it gives some golden info on influencing peoples decisions, and can be applied to all these areas. Time to split test some of these ideas 
Skip to the 5 minute point
Dan Ariely asks, Are we in control of our own decisions? | Video on TED.com

Skip to the 5 minute point
Dan Ariely asks, Are we in control of our own decisions? | Video on TED.com