Human minds are associative in nature, so the order in which we receive information helps determine the course of our judgments and perceptions. For instance, the first price offered for a used car sets an ‘anchor’ price which will influence how reasonable or unreasonable a counter-offer might seem. Even if we feel like an initial price is far too high, it can make a slightly less-than-reasonable offer seem entirely reasonable in contrast to the anchor price.
Be especially mindful of this bias during financial negotiations such as houses, cars, and salaries. The initial price offered has proven to have a significant effect.