What’s so hard about good habits?

One of the hardest parts about getting into 'Getting Things Done' is breaking the bad habits and vices which keep you unproductive. For some reason we find it much easier to adopt bad habits as opposed to developing good practices. This morning I was wondering why it was that quitting my morning Dunkin Donuts trip was so hard - especially when less than a year ago I didn't drink coffee.

Between last year and this year nothing really had changed. There's always been two donut shops between home and work but until last summer I had never even considered stopping at them. For some reason during the summer I got myself hooked on Ice Coffee (I still don't drink hot coffee) and have been grabbing one every morning since.

I'm not going to bash coffee (for fear of the Arabica gods striking me down) but I am curious why it was so easy for me to start drinking something I had previously never craved. As I continue to fight my $1,092 a year coffee habit (3 bucks a morning * 7 days a week * 52 weeks = $1092 dollars) it maked me wonder: why is it so hard to develop good habits but so bad to develop bad ones?