If we think we can do it, we can

"If you wear a white coat that you believe belongs to a doctor, your ability to pay attention increases sharply. But if you wear the same white coat believing it belongs to a painter, you will show no such improvement." 

Our world is full of advice that relates to things like this. "You need to dress the part to look the part". Whether it's for a job interview or spending a day at the office or even going on vacation, we're expected to dress in a certain way to give off a certain vibe. 

Interestingly enough, though, following the self-fulfilling prophecy, when we think we look the part, we end up thinking we're closer to what we want to be. This is similar to selective perception, where our expectations influence what we see in the world, except with the self-fulfilling prophecy, what we expect is what influences our actions. As the name suggests, we will act to fulfill what we're expecting to happen to us. 

So, if you wear a white coat that you think belongs to a doctor, and therefore you think you look like a doctor and in that way closer to being a doctor, you are more likely to take on traits that you think a doctor has. If you think they are incredibly smart and able to pay attention to many details, you're probably going to do better on a test than someone who was given a different idea about the coat. If you don't think the coat belongs to someone incredible smart and perceptive, you won't have those affects when you wear it. 

This is similar to the example of an experiment where after being told the fact that girls are worse at math, the group of girls did worse. They were good students, just like the group that wasn't told this fact, but after being told the statement "girls are worse at math than boys" they did much worse on their tests. If you begin to think you can't do it, you're more likely to not be able to do it.