I wanted to link to this yesterday. Jeff Cornwall talks about using culture as a hiring criteria, and the difficulty people have using it as a firing criteria.
Firing employees because they do not fit in a culture is where many, especially those in a corporate environment, get uncomfortable. They seem to hope that eventually these employees will just realize that they do not fit in and leave on their own accord. But, in a small business we do not have the luxury of keeping any excess employees.
Performance in a small business is more than just doing one's job. The culture of the business is still a work in progress, and the business owner must be diligent to make sure that it is evolving the way they want it to. Just because a salesman meets his quota is not enough to keep his job. If he does so in ways that undermine the way the owner wants to build relationships with customers that can be just as important a criterion for continued employment as selling product.
It may be a soft criteria and it may seem subjective to an outsider. But, an entrepreneur knows how she wants her business to run and she has an obligation to make the tough decisions to make sure that the culture develops in a way that is consistent with her values, her ethics and her vision.
I think it is human nature to think that people can change. It's true, people can change, but it's usually not because of something you did. I'm not saying you shouldn't give people a chance, but the saying "slow to hire quick to fire" may be good advice in situations like this.