Given ample opportunity to rise during a bull market, the failure of a particular issue to move upward in gear with the averages can be warning enough in itself that something is wrong. Laggards are losers.
Speculative flings in search of “something that hasn’t moved yet” can sometimes sweep up a laggard issue or two, but by and large, the hope is that what did not happen yesterday and today will happen tomorrow– only because the market seems so marvelous– and as the bull surges on without that stock, the reality becomes progressively more urgent: a stock does not have to go down first to show that it is becoming weak. Merely not going up is, under most bullish circumstances, a sign of trouble brewing.
– Justin Mamis, When to Sell