Humans’ blind spots are predictable: There are certain types of traits where people can’t see themselves clearly, but others where they can. The psychologist Simine Vazire asked people to rate themselves and four friends on a bunch of traits, ranging from emotional stability and intelligence to creativity and assertiveness. Then, to see if they had predicted their own personalities better than their friends had, they took a bunch of tests that measured these traits.

The good news: You have some unique insight into your emotional stability. In the study, people outperformed their friends at predicting how anxious they’d look and sound when giving a speech about how they felt about their bodies. But they did no better than their friends (or than strangers who had met them just eight minutes earlier) at forecasting how assertive they’d be in a group discussion. And when they tried to predict their performance on an IQ test and a creativity test, they were less accurate than their friends.

People know themselves best on the traits that are tough to observe and easy to admit. Emotional stability is an internal state, so your friends don’t see it as vividly as you do. And although people might not want to call themselves unstable, the socially acceptable range is fairly wide, so we don’t tend to feel terribly anxious about being outed as having some anxiety. With more observable traits, we don’t have unique knowledge. If you’re a raging extrovert or a radical introvert, we don’t need to ask you—we can pick it up pretty quickly from your impromptu karaoke performances or your complaints that your husband types too loudly. And with the most evaluative traits, you just can’t be trusted. You probably want to convince everyone—and yourself—that you’re smart and creative.

This is why people consistently overestimate their intelligence, a pattern that seems to be more pronounced among men than women. It’s also why people overestimate their generosity: It’s a desirable trait. And it’s why people fall victim to my new favorite bias: the I’m-not-biased bias, where people tend to believe they have fewer biases than the average American. But you can’t judge whether you’re biased, because when it comes to yourself, you’re the most biased judge of all. And the more objective people think they are, the more they discriminate, because they don’t realize how vulnerable they are to bias.

Any time a trait is easy to observe or hard to admit, you need other people to hold up a mirror for you. Romantic partners and close friends might be more informed, because they’ve observed you more—but they can also have blurrier vision, because they chose you and often share that pesky desire to see you positively. You need people who are motivated to see you accurately. And I’ve come to believe that more often than not, those people are your colleagues. The people you work with closely have a vested interest in making you better (or at least less difficult). The challenge is they’re often reluctant to tell you the stuff you don’t want to hear, but need to hear.