Exactly! Sometimes for a stock there is a period of no trading, and the movement could go either way. If the sellers hold their ground, in many cases, the bid will rise to meet the ask, and if there is good news, or the stock has a low float, the odds are that the buyers will eventually "hit the ask", moving the pps upwards.
But if one seller sells at the market, hitting the bid, it can have the effect creating an atmosphere of lack of faith in the stock and it's current PPS, and it will inspire other sellers to hit the bid before the PPS drops any lower.
This is especially true of a low float, low volume stock. One good bidwacker can have a negative impact on the PPS that could last for hours, maybe longer.
The effect is less pronounced in a high volume, momentum play that is in great demand. However, if too many bidwackers start 'hitting the bid', it can nevertheless kill a rally.
Ironically, it is exactly during a high volume day for a popular stock that it is easiest to set one's price and sell at the ask. However, most new traders are not aware of this.
Of course there are times when a market order is necessary, as when there is a sudden collapse in the PPS and you feel the need to sell in order to protect whatever capital you have left. In those cases, a market order - or 'hitting the bid'- may be the only way to get out of your position quickly.
News 
Market Data 
Discover 
