As a leader, simply holding positive expectations about team members' performance can actually lead to better team performance. Research has clearly shown the power of holding positive expectations of others. We get the outcomes that we expect. This is what is known as the "self-fulfilling prophecy," or the "Pygmalion effect" - named after George Bernard Shaw's play in which Professor Henry Higgins transforms a common flower seller, Eliza Doolittle, into a lady because he believed that it would happen (you likely are more familiar with the musical version, "My Fair Lady").
The power of the Pygmalion effect, first captured by psychologist Robert Rosenthal in his study of elementary school children, has been well documented as a simple and effective way to boost performance - in the classroom, in the workplace, in the military, and elsewhere.
In his famous study of elementary school students, Rosenthal led teachers to believe that certain pupils in their classrooms had been identified as "intellectual bloomers" - children who would show an intellectual growth spurt during the school year. In actuality, the students were randomly given the designation of intellectual bloomers, but at the end of the term, these students did indeed show higher academic achievement. Why? Because the teachers believed in them. How? Later studies showed that teachers unconsciously gave more positive attention, feedback, and learning opportunities to these students. In short, teachers were able to "nonverbally" communicate their positive expectations for academic success to these students.