William Eckhardt in The New Market Wizards … I have to re-read his chapter from time to time when things start to go awry in my own trading:

“Are there any other natural human tendencies that you think tend to sabotage success in trading?”
“There is what I refer to as ‘the call of the countertrend.’ There's a constellation of cognitive and emotional factors that makes people automatically countertrend in their approach. People want to buy cheap and sell dear; this by itself makes them countertrend. But the notion of cheapness or deamess must be anchored to something. People tend to view the prices they're used to as normal and prices removed from these levels as aberrant. This perspective leads people to trade counter to an emerging trend on the assumption that prices will eventually return to ‘normal.’ Therein lies the path to disaster.”