Provide a good reason to leave the company

Assume you found another job and you will need to provide a reason for leaving. What is the best reason to provide? (if anything goes wrong with your new job you could go back assuming that you gave a good reason)

-If my reason was "looking for new challenges"...& the new job goes wrong...it wouldn't make sense to return to the old company because they know you will run away after a couple of months

-If my reason was "looking for a job closer to home"...& the new job goes wrong...it wouldn't make sense to return to the old company since they will know I will be looking for jobs closer to home

You know what I mean? I've seen a lot of profiles on LinkedIn where people leave for 4-6 months then return to their original company.