Once hired you must give someone the opportunity to be successful. This means communicating clear expectations about what success looks like in the organization. This should include behaviors as well as tasks. From there the employee has the opportunity to make an informed decision about whether they will or can conform. If they are not able to meet the standards they may self-select out or you will need to terminate. A person who doesn't fit is uncomfortable themselves and creates dissonance amongst your team. They can not stay. Going forward make sure to use great behavioral based interviewing questions so that future hires are a better fit.