I haven’t watched American Idol in years, but I still remember the cringe-worthy auditions of those who claim to be the next Idol yet can’t carry a tune to save their lives. For some, it’s hard to objectively evaluate their own talent when there is so much at stake.
Psychologists have coined the term “motivated reasoning,” a tendency for people to reason in ways that allow them to form or maintain desirable beliefs (e.g. that they can sing). They may readily accept information that supports their beliefs as valid but question information that challenges their beliefs (remember how angry those contestants were at the Idol judges?).
In a similar vein, research should not be conducted by those who have a stake in how the research findings turn out. This may seem obvious, but I’m surprised by how often it still happens.