Do you think there is something that is not meant to be even though we strive so hard for it?

Did you ever heard anyone said that, esp your family when you din get what you want. Well, i heard from my lecturer. She said sometimes you have to change you way cause maybe you are not meant to be something. I thought that is so ridiculous. Even when you work so hard to become something, and it din work out, you still need to move on. Although two sensitive issues will get in our way; time and money. If there is something like that, well where is the border line. When should I stop? When should we stop?