No one can promise you that...

No one can promise you that your life will be easy.

No one can promise you that you'll never feel pain or/and sadness.

No one can promise you that you'll never lose someone you really love.

No one can promise you that the person you love/like will love/like you back.

No one can promise you that you'll always get what you want.

No one can promise you that everyone will like you.

No one can promise you that you won't lose a friend you really care about or your best friend.

No one can promise you that no one will ever lie to you.

No one can promise you that you'll get married with the right guy/girl.

No one can promise you that the one you like/love will not play with you or cheat on you.

No one can promise you that your relationship with her/him will work out.

This can go on....

Okay they can promise you these things I just said but they would be stupid to do so. They would have to break their word eventually and will most likely not be able to make it happen.