What makes some more sensitive to Betrayal than others?

Like when someone's other half cheats on them....they might break up and not date again for years over the betrayal and loss...or during a business transaction when the other party lies, they loose their mind, call the deal off, and not by whatever they intended from anyone due to the betrayal they feel....as opposed to...the other extreme might just take it in stride, smile and say "Good One"...and then other's are a bit of each...what makes one so sensitive?|||trust!! trust is earned not given. and when it's broken, despite by who or when or how, it hurts and its even harder the next time to trust again!! its not being "so sensitive". its about OTHER people NOT being sensitive enough or care enough and take the other person for granted.