When you have cried wolf too many times, people will stop believing you. This is so even if you change tune and insist there is no wolf after all. This is the problem with John Tsang Chun-wah. Since the government announced a massive multi-year injection of public funds into the mostly self-funded Housing Authority, the finance chief has surprised everyone by saying it's all affordable because we are likely to have three years of surpluses. But this is from a man who has been a consistent (and false) prophet of government deficits. Don't get me wrong. The government plan to build 290,000 public flats in the next decade is laudable. (I would, though, start cracking down on wealthy public tenants, but that's a different story.) It's clear the authority doesn't have the money for such a drastic expansion of public housing supply. So the plan is to inject future public investment income into a new housing reserve fund over several years. The plan should benefit grass-roots groups and low-income families. Its justification goes beyond short-term yearly projections of fiscal surpluses or deficits. Can we afford it? Of course we can, with our more than HK$2 trillion in reserves. But Tsang has zero credibility when it comes to budget forecasts. Since his appointment in 2007, he has never delivered a single accurate forecast. In some years, the surprise surpluses were so enormous he had to give them away as one-off sweeteners. He feints outrage in his most recent blog that the three-year surplus guesstimate is based on "public budget projection", not "personal conjecture", as if such projection is a science. Indeed, his budget forecasts have more to do with ideology than science. Our government has always been against "welfarism". Citing the need for "financial prudence" or playing Scrooge helps keep a lid on public spending - hence the consistent cry of the deficit wolf. But it's now clear the government has Beijing's backing as increasing cheap housing supply is seen as a way to moderate public discontent. Tsang may have changed his tune, but people may be forgiven if they are sceptical.