Can't vs. Don't

I'm doing this online course about Social Psychology (still obsessed with those free online courses! nerd!) and I read about an interesting study the other day.  Its basically saying that when you are trying to change your habits - using the words "I can't" versus "I don't" can make all the difference. So, say you are trying to exercise consistently but you are slacking one night...you are more likely to fail if you say to yourself, "I can't miss a workout tonight" instead of "I don't miss work outs".  Or "I can't eat this sugar!" versus "I don't eat sugar".  They ran studies on several groups of women and the groups who told themselves that they 'don't' do something always had much higher percentages of participants who met their goals.
What do you think? I think we are very used to ignoring 'can't' messages to ourselves...but its a little more ballsy to defy the 'don't' messages. I've been trying this with running and it has definitely worked! What would you try it on?