Contrary to the wisdom in self-help books, sky-high expectation is mostly met with crushing disappointment. Take Sina, China’s second-biggest news portal. It trades at a frothy 47 times this year’s earnings. The hope? That Sina Weibo, its Twitter-like microblog, will start generating enough sales to save its parent from an otherwise maturing business.

The reality, however, is that Sina’s average annual sales growth rate has halved over the past three years compared with the prior three as advertising spend shifts away from display advertising to online video and search. And Sina has warned investors that advertising sales will be down by a quarter in the first three months of this year, versus the end of 2011. This is a traditionally quiet period, but the drop is twice that seen in the last two years.

Charles Chao, chief executive, promises that Weibo (meaning microblog) can make revenues by the second quarter. But those sales are to be led by advertising to computer users, even though he admits that there are more mobile users.