I know a lot of people who don't pull their own weight: children, husbands, wives, co-workers, team members. Eventually the others on the team get tired of pulling more than their own weight, and the team starts to falter. Sometimes it fails catastrophically.
In my rowing days there was something extraordinary about knowing that there were no passengers on board the boat. As a crew, we knew with unwavering certainty that every one of our fellow crew members could be counted on totally to give his all every time we raced. One of the principal reasons our boat went fast - very fast - was because every one of us committed to giving his very best all the time, so no one believed that he was being asked to do any more than his fair share.
You can't ask much more in any team. Whether it is a team of two in a relationship, or four or five in a family, nine in a rowing boat, eleven in a football team or forty in a workplace, if everyone simply gives to the best of his or her ability, the team will perform up to and beyond expectations.