That's probably true although I know a chap who at one point was borrowing money on his credit cards to trade, and is now worth a healthy 7 figures.
You're chances of making a living off £20k are slim, no question, but given enough time and perseverance, a £20k account could become something considerable. There's a difference between cautious and blind optimism, and sometimes there's too much negativity about the outcome of trading. If you're convinced you're going to fail, you probably will (there's also a Seykota quote along these lines).