Humans are given to linear extrapolation of existing trends....

Humans are given to linear extrapolation of existing trends. When a share's price is trending up, forums are full off cheerful banter and 'how high can it fly' comments. And when a share is trending down, people try to surpass each other with doom and gloom and 'how low can it go' comments, the more pessimistic ones usually predicting a future share price of zero.
That's fair enough to a point, but linear extrapolation of existing trends has predicted that New York City would be covered in a 20-metre layer of horse manure by 1930...and then the motor vehicle came.
Having said that, I wouldn't mind actually seeing a change in trend here.