Q: "How can you know something is for you but not be ready for it?"
A: That can be a bit of a loaded question depending on the context, so I'll go with the more vague, general approach. There are levels. When we receive visions, vivid pictures are then painted and we see them so clearly mentally but they haven't yet made it over to reality. When a baby is born, that baby isn't born walking. There are stages. Building must occur. Work must be done.
Now, there is also a difference between just not being ready and preparing. Sometimes we stop at "I'm not ready," or "I'm not perfect." We tend not to include the "yet" because we aren't doing what is required of what is for us. Our reasons vary, and sometimes we have no reason at all. It is a choice to not make yourself ready and allow your destiny to pass by you.
You want the job but haven't written a resume or even applied.
You want the girl but haven't shown any interest or shown that you have your stuff together.
You want the car but don't know how to drive.
You want but you don't do, therefore you don't truly want. The bottom line is that we do what we want. (There are very few exceptions to that rule.) When we aren't ready yet, we get in the waiting position and simultaneously take proper steps to prepare. It's for you. You coming for it or nah?
If no one has shown you today, I love you but God loves you better.