The day your home goes on the market, there are already qualified, motivated buyers whose criteria match your home. So when your home hits the market there may be multiple offers from potential buyers. Often these are buyers have already made offers on other homes and got beat out by a competing offer. When it is priced and marketed correctly, particularly in an active market cycle these buyers will act quickly because they do not want to risk losing the home to another buyer.
There is a correlation between time on the market and the property getting top value, but not the correlation many sellers think. Generally, the longer it takes, the less the seller will procure for an offer price. Why? Because of the WWWTH Syndrome: "What's Wrong With That House?" If the property has been on the market for an extended period of time, buyers begin to wonder why no one has bought that house. The answer may be nothing other than being over priced. The result is often lower offers or no offers.
The importance of effective marketing is to put your home in front of the highest number of qualified buyers and buyer's agents and present it in the best possible manner to get full market value for it. The reality is that while good marketing is important, it does not make your house worth more than what it is worth in any market cycle. Hence why, even in a good market for sellers, prices still get reduced or overpriced homes don't sell.
It is statistically proven that the longer a house sits on the market the lower the offers it will get, reductions or not. When new buyers come into the market, they want the fresh inventory, not the stale listings that all the previous buyers rejected. Your home becomes a "been there, done that" property, making buyer's agents and buyers much more likely to submit lower offers, or even worse, pass it over completely.