1. I'm sure you will be a good author.

2. I'm sure you would be a good author.

3. I'm sure you can be a good author.

4. I'm sure you could be a good author.

(What is the difference among them in meaning?)

will = something that will definitely happen

can = the person has the ability to be a good writer (but nothing is said about whether he/she wants to be!)

would and could = possibilities (nothing said about ability or certainty)