Leaving a startup you founded is a big decision to make. There are several reasons you can tell your investors as to why you want to leave. All are "acceptable" in terms of their view of you. These include:
- The company is moving into a different stage and my skill set does not match anymore
- You have another opportunity that you cannot pass up.
In terms of approaching your investors about leaving, that can be a little tricky as well. The best thing to do is to take on lesser and lesser responsibility and get others to gradually do what you do. That way, the transition will be a lot smoother. Now, this takes some time to do right but as long as you have a plan, it is manageable.
Another thing a founder exiting does is create a lot of anxiety for employees. This is unavoidable and needs to be dealt with. One good way to do this is to remain on an advisory board and tell the employees that your decision to leave is a personal thing that you struggled with.
Don't be afraid of this. This happens all the time. You should be able to exit gracefully and not have any hard feelings as long as you are sensitive to the needs of the company and make every attempt to set them up for continued success.