You built an interview guide, used structured interviews, wrote the perfect behavioral interview questions, and used an interview scorecard. Yet, you still hired someone who was a poor fit for your organization. With the right tools, you can reduce the chances of this happening, but it still can happen. Anyone who hires people ends up making mistakes. Please don't beat yourself up about it. Hiring the wrong person for a job feels awful. But, it is a mistake that everyone makes. The important things are what you do next and what you learn from it.
Being a good manager and decision maker means knowing who and when you need to fire someone. You must be able to recognize your mistake. The earlier, the better. The inability to see you've made a poor hire compounds the error. The longer the person is in the position, the more damage they'll do. We all think of the opportunity cost of having the wrong person in the job (how much more productive would the right fit be?). Even more so, the people who need to go are those who damage team morale and drag down the team and the company like a weight. The more the lack of contribution becomes apparent to others, the more the employee is likely to engage in politics and obfuscation to keep their job and gain power, and the more destructive this will be to your team.
The most challenging time to identify a bad hire is early. There is a natural inclination to believe in the person you just hired. You haven't had enough time to see the lack of productivity. There were reasons you hired them, and even if everything isn't perfect, it is natural to continue to believe in those reasons and excuse the warning signs.
It is crucial to empower and believe in your employees. In addition, they need to feel it is okay to take risks and make mistakes. So the tricky thing is believing in your new employee, empowering the employee to feel safe taking risks, and evaluating whether they have fatal flaws that will not work in your organization. This is tricky. If critique dominates your thoughts and communication, the employee will sense it, and you may be undercutting an excellent fit. On the other hand, if empowerment keeps you from evaluating, the poor fit will last too long and do too much damage.
Eventually, it will become evident to everyone that the lousy fit needs to go. By then, there has been incalculable damage to the organization. If you haven't acted by then, many will wonder if you can see your mistakes and make difficult decisions. Don't wait that long. Don't hold on to someone because someone has to fill the role. Removing a bad hire will increase productivity, and you'll find a way through. Talk to HR and get legal consultation if needed, but do it now. Don't wait until more damage is done.