Laziness

I recently discovered that I'm exceedingly lazy when there's someone else around to do the job. When I'm the only one available to help, however, I'm more than happy to go above and beyond the call of duty. There are many examples. The simplest perhaps is related to cleaning. I'm happy to clean my apartment. In fact, it bothers me if it's messy or dirty. (Of course this doesn't mean that it's never messy or dirty.. it often is).
When I have a roommate, the level of responsibility I feel decreases dramatically. I've been told that I'm a good roommate (everyone except for neat freak roommates have thought so).. I've gotten much better since the days of living with my family about taking care of shared spaces. However, when I have a roommate, I do my share of work only because I don't want to displease the other person.. not because I care about having a clean house.
I wonder if it partly stems from a subconsious lack of confidence in my abilities (not just for cleaning, but taking care of another person, or taking initiative on a big project, etc). Perhaps I'm lazy because I think that someone else can do the task at hand better than I can. Part of it is also from growing up in a large family, where it's so easy for everyone to blame one another for chores left undone instead of taking the two minutes to, say, take out the trash.
I'm not sure what to do about this, except to catch myself whenever I have the urge to let someone else take responsibility and force myself (without the forced attitude of course :)) to do whatever needs to be done immediately and without thought.