What makes someone who they are?
Each person has an idea of his/her own personality type — if they are bubbly or reserved, sensitive or thick-skinned. Psychologists who try to tease out the science of who we are define personality as individual differences in the way people tend to think, feel and behave.

There are many ways to measure personality, but psychologists have mostly given up on trying to divide humanity neatly into types. Instead, they focus on personality traits.
The most widely accepted of these traits are the Big Five:

• Openness – Openness is shorthand for “openness to experience.” People who are high in openness enjoy adventure. They are curious and appreciate art, imagination, and new things. The motto of the open individual might be “Variety is the spice of life.” People low in openness are just the opposite: They prefer to stick to their habits, avoid new experiences and probably are not the most adventurous eaters. Changing personality is usually considered a tough process, but openness is a personality trait that’s been shown to be subject to change in adulthood.
• Conscientiousness – People who are conscientious are organized and have a strong sense of duty. They’re dependable, disciplined and achievement focused. You won’t find conscientious types jetting off on round-the-world journeys with only a backpack; they’re planners. People low in conscientiousness are more spontaneous and freewheeling. They may tend toward carelessness. Conscientiousness is a helpful trait to have, as it has been linked to achievement in school and on the job.
• Extraversion – Extraversion versus introversion is possibly the most recognizable personality trait of the Big Five. The more of an extravert someone is, the more of a social butterfly he/she is. Extraverts are chatty, sociable and draw energy from crowds. They tend to be assertive and cheerful in their social interactions. Introverts, on the other hand, need plenty of alone time, perhaps because their brains process social interaction differently. Introversion is often confused with shyness, but the two aren’t the same. Shyness implies a fear of social interactions or an inability to function socially. Introverts can be perfectly charming at parties — they just prefer solo or small-group activities.
• Agreeableness – Agreeableness measures the extent of a person’s warmth and kindness. The more agreeable someone is, the more likely he/she is to be trusting, helpful and compassionate. Disagreeable people are cold and suspicious of others, and they’re less likely to cooperate.
• Neuroticism – Neuroticism is a trait characterized by sadness, moodiness, and emotional instability. Individuals who are high in this trait tend to experience mood swings, anxiety, irritability, and sadness. They experience a lot of stress, have worries about many different things, gets upset easily, experience dramatic shifts in mood and struggles to bounce back after stressful events. Those low in this trait tend to be more stable and emotionally resilient, they deal well with stress, rarely feels sad or depressed, doesn`t worry much and are very relaxed.

Conveniently, you can remember these traits with the handy OCEAN mnemonic (or, if you prefer, CANOE works, too). The Big Five were developed in the 1970s by two research teams. These teams were led by Paul Costa and Robert R. McCrae of the National Institutes of Health and Warren Norman and Lewis Goldberg of the University of Michigan at Ann Arbor and the University of Oregon, according to Scientific American. The Big Five are the ingredients that make up each individual’s personality. A person might have a dash of openness, a lot of conscientiousness, an average amount of extraversion, plenty of agreeableness and almost no neuroticism at all. Or someone could be disagreeable, neurotic, introverted, conscientious and hardly open at all.