Politicians only get to the top because they have no qualifications to detain them at the bottom.

Peter Ustinov (1921–2004) English actor, author, director

(Attributed)

Ustinov apparently used the phrase several times, with slight variations.

• As quoted above, in International Celebrity Register (1959) [ed. Cleveland Amory]
• Also appears in Ustinov's article, "Politics and the Arts", The Atlantic, Vol. 218 (1966)
• "People who reach the top of the tree are only those who haven't got the qualifications to detain them at the bottom." -- Interview with David Frost (1969)
• "I believe those who rise to the top of the political tree just didn’t have the qualifications to detain them at the bottom." (Source)