Tyler Cowen notes a study that shows that the promise of a reward for behavior distorts our perceptions of that behavior.
When you know you might be paid to eat an insect, you sample more “yum-pro-insect” propaganda, and you interpret it more favorably. Furthermore subjects do not in advance predict these self-persuasion effects. So “bait and switch” marketing techniques may succeed in warming individuals up to ideas, even if the promised prize is eventually yanked. (Source)
On a less disgusting note, consider someone who is asked to move to Detroit as part of a job promotion. In an ideal market they would weigh the downsides of moving to Detroit against the upsides of the raise ad promotion. In reality, the promise of the raise will push them to notice net-positive information about Detroit and miss negative information.
As Cowen notes, the perceptions may continue to exist, even if the prize is yanked. So, for instance, if suddenly the job is not going to pay more it will not change the impression we have built up about Detroit as a place to live.