Quiet markets are where most discretionary damage occurs. The setups are absent, the standards slip, and a trade appears mainly to make the afternoon eventful. Losses from boredom are usually small individually and large in aggregate, which is why they survive unnoticed for months.
The underlying driver is that trading is intermittently rewarding, so the absence of action feels like withdrawal. It has more to do with stimulation than with money, which is why boredom trades are often taken in instruments the trader does not normally follow.
The fixes are structural. Define the hours you trade and close the platform outside them, use alerts instead of watching, and put a genuine second activity in the dead period - review, replay, research - so that the alternative to trading is not nothing.
Related: forced-trading, action-bias, overtrading, patience