It does, because people's preferences do not obey the rules of rationality. They differ inconsistently across different time-scales, so that it's very common (

It does, because people's preferences do not obey the rules of rationality. They differ inconsistently across different time-scales, so that it's very common (eg) to have a very strong desire for something immediately gratifying (a cigarette, more ice cream, whatever) and a weaker desire to not want them. This is a fairly well-studied phenomenon; you can [start here](http://picoeconomics.org/breakdown.htm http://picoeconomics.org/breakdown.htm) with the work of George Ainslie.