Some people tell me that we professional players are soccer slaves.Well, if this is slavery, give me a life sentence.

-Charlton, Sir Bobby (Robert)
  Quoted in Peter Ball and Phil Shaw The Book of Football Quotations (1989).

It might have been supposed that competition between expert professionals, possessing judgement and knowledge beyond that of the average private investor, would correct the vagaries of the ignorant individual left to himself. It happens, however, that the energies and skills of the professional investor and speculator are mainly occupied elsewhere. For most of these persons are, in fact, largely concerned, not with making superior long-term forecasts of the probable yield on an investment over its whole life, but with foreseeing changes in the conventional bias of valuation a short time ahead of the general public† This battle of wits to anticipate the basis of conventional valuation a few months hence, rather than the prospective yield of an investment over a long term of years, does not even require gulls amongst the public to feed the maws of the professional; it can be played by professionals amongst themselves.

-Keynes (of Tilton),John Maynard, 1st Baron
  The General Theory of Employment, Interest, and Money.

It is this tendency to play with manic enthusiasm on every possible occasion that distinguishes the amateur jazz musician from the professional, often to the public detriment of the latter, who are regarded as snootyand unfriendly.

-Lyttelton, Humphrey Richard Adeane
  Why No Beethoven?, ch.1.

It is the professional duty of the advertising agent to conceal his artifice.When Aeschines spoke, they said, 'How well he speaks', but when Demosthenes spoke, they said 'Let us march against Philip.'

-Ogilvy, David
  Confessions of an  Advertising Man, ch.5.

  The only reason for being a professional writer is that you just can't help it.

-Rosten, Leo Calvin
In D L Kirkpatrick (ed) Contemporary Novelists (1976).