You are a very modest person by nature, so you do not let people in on your secrets easily. This trait of yours also helps you dutifully keep other people’s confidence. However, if a secret you are asked to keep concerns something sticky or even illegal you will most certainly never agree to keep it.
Private matters present no such problem – you’d easily honor, say, a request not to tell anyone about a child given up for adoption, especially if it’s its mother who asks you to keep the secret. And if you gave your word you’ll stay true to it no matter what.