First impressions are everything these days. If you can perform well enough (or bad enough) just long enough for people to think they have you figured out, that impression will stick like glue. The best current example of that is Aledmys Diaz.
Diaz started strong in April, leading the Majors in batting average and slugging. He somehow still failed to win either NL Player of the Month or NL Rookie of the Month. But after a month of complaints about where Diaz bats in the lineup, Mike Matheny finally made the decision to promote Diaz from his regular eighth spot in the lineup to second, arguably the most important position in the lineup.