As stated, this is merely a truism, and you have not justified this belief. Would you care to? It seems very irrational to me. High office is one of the most difficult and most impactful jobs in the world. It's easy to do a terrible job and screw everyone over while enriching yourself, of course, but extremely challenging to do a good job. You are responsible for the fate of tens or hundreds of millions of people, and must exercise incredible judgment on the breadth of every macro problem society faces while simultaneously maneuvering both internal support and foreign relations. Why would we not want to make this most important of all jobs a job where people can actually grow into the role and demonstrate expertise in it? You are strictly only eliminating the electorate's options. There is already a corrective mechanism for voters to evict someone doing a bad job [whether they choose to exercise it is another matter, but that's literally democracy in action], but there should be no mechanism to sustain a job well done?