"Your siblings are your first contact with the world you live in," Dr. Greif says. "You usually have up to 18 very intense years living together, so they give you a natural sense of how you're doing in relation to the world." You're also more likely to compare yourself to people who are similar to you, like your siblings, explains Susan McHale
, PhD, professor of human development and family studies at Penn State University. "Social comparisons don't always make you feel badly; they can make you feel strong and confident, too," she says. Though we don't actually know how the Kardashians interact when the cameras aren't rolling, KUWTK
episodes would suggest that they all still spend a lot of time together, even as adults with their own kids and families, so those relationships could be even more intense.