When we look back on past relationships, it can sometimes be hard to pinpoint exactly what went wrong.
Whether we feel like the other person was too needy, too distant or we were the ones who made things difficult, it's not always easy to see why two people didn't work out.
But a popular book called Attached attempts to explain why some relationships thrive while others don't go the distance.
Watch: The Mamamia team confess our relationship deal-breakers. Post continues below.
Written by psychiatrist and neuroscientist Dr. Amir Levine and Rachel Heller, the book explores how we have a genetic need to be in close relationships with other people because it makes us stronger.
And they do that by looking at a concept called attachment theory.
It sounds like something you'd find in a old high school textbook you were supposed to read, but the theory actually explains a lot about how we behave in relationships and what we look for in a partner.
First defined by British psychiatrist and psychoanalyst John Bowlby, attachment theory suggests that we behave in three distinct ways when it comes to relationships; secure, avoidant or anxious.