Quote from Daal:
TF claim a uptick/downtick is more likely to be followed by another uptick/downtick. This defies economic theory where higher prices bring about supply and decrease demand and lower prices create demand and decrease supply, if markets werent mean reverting by nature, that is if they were more or less random but with a bias of going to whichever direction they recently headed you would have absolute gigantic mispricings(like a stock market with a normalized PE of 1000). The reason that doesnt happen is because economics kicks in and prices mean revert
Now you might claim you can capture the 'middle' moves with a system that worked historically, and perhaps that is true, whether it will keep working who knows, but the TF claim that higher/lower prices are more likely to be followed by higher/lower prices is not correct most of the time
Agree with what you are saying in terms of mean reverting nature of the markets.
However, I would tend to have a slightly different definition of underlying trend following concept
In my opinion, (and you can see how I explained it here) price market distributions are leptokurtic - which simply means that large trends will occur more frequently/at a larger magniture than the normal distribution would suggest. As a result, if you try to get on all the trends, you will necessarily ride all the huge ones. This will provide the bulk of the returns, offsetting any losses that might have occurred in the random/mean reverting periods where trends reverse too quickly.
So, an uptick/downtick is not more likely to be followed by another uptick/downtick (ie the market is more frequently mean reverting) but this is just one parameter of the equation (ie Win %)... You also have to take into account Avg Win / Avg Loss to calculate expectancy.
I believe that Trend Following's underlying concept can be summarised by:
if you follow all trends, despite the predominant mean reverting characteristic of the markets, big trends/wins will arise infrequently and produce more returns than the losses incurred most of the time (ie positive expectancy despite lower probability).