I thought of not writing about sideways markets because generally, traders hate sideways markets and most of the traders love to know where the fast price action happens.
Anyways here we go,
What is a Sideways Market?
The sideways market occurs when markets are not dominated by the large players and instead traders attempt to dominate the market and keeps the market in a stable range. These are the phases where breakout failures are very common.

If you are a trader out there then the real skill is not only identifying and trading successful breakouts but also the breakout failures. Frequent opportunities in the markets are breakout failures than the successful breakouts. Hence the reason why most of the trend following systems has a win rate between 35-50 in the lower time-frame.
Sideways markets are more of a highly competitive field among traders and it is the survival of the fittest and the big traders are clearly not active in these zones. such zones are more of a predatory setup zone where more of entry-level traders fall prey to the highly experienced traders.
There are zones where I had observed the sideways markets which goes more than three to four months is where the breakout traders lose everything back to sideways markets.
We are told that 70% of the time market goes sideways then why only fight for the 30% of the trend? Why not to develop skill to trade the sideways markets.
If your understanding of the sideways markets increases probably your knowledge about trend trading increases a lot.