The days have just started to lengthen, it's the time for vague notions of New Year, New Me. All it takes is a bit of willpower - setting us up perfectly for failure a few days or weeks down the road.
Exercising willpower is enormously difficult - not because we are weak, but because the effort required to change our habits is big. There's also a myriad of subtle environmental influences that can knock our good intentions off course.
While it might feel as if we have failed when we let our gym membership lapse and hit the chocolate, there are some very good reasons why this might be so. And knowing about them might just give us the edge and allow us to make real change.
Michael Blastland returns with The Human Zoo, exploring and exposing what makes us tick.
Producer: Toby Murcott
A Pier production for BBC Radio 4.