Why is it so easy to break promises to myself?

I give it my all when I give my word to someone else - but I find that I'm constantly breaking promises to myself in favor of doing things for others.  I think it's just one symptom of the way that I'm NOT taking care of myself at the moment and feeling sick & tired because of it.  Such a vicious cycle to be caught in.  I read a blog [the title escapes me at the minute] where the blogger made a few promises to herself.  Things that she wanted to accomplish between Feb 2011 & Feb 2012.  I'm thinking of adapting this concept - only I would do it from 5/11 thru 5/12...being that this is already the 2nd day in May!  Boy how time flies!  I'll have to think about what I'd like to do/accomplish for me in the next year.