Employees do sometimes move on, much as you would like the great ones to stay and grow. Your business changes all the times as it matures and grows. This means your employee requirement changes also. When an employee leaves your business, it really is a good opportunity to get feedback from them on their experience in your business, with a view to step up in the future, rescope their role before recruiting and perhaps reexamine your person specification. Two people in the same job will not deliver the same output. The more structure you put in the role, the greater your success in getting results from employees is likely to be.
Use this exit interview template with every employee who leaves. You will find helpful information across the collective interviews.