Did you ever wonder why your best friend is ready to move in with her new boyfriend after three dates, but it takes you three years before you’re finally able to say the “L” word? It all comes down to attachment, a theory first developed by British psychoanalyst John Bowlby way back in the dark ages (um, we mean the 1950s). Originally developed as a framework to understand the relationships between infants and their parents, the attachment theory has more recently been expanded to provide insights into relationships and friendships between adults. Here’s the lowdown.