The thing about science is, you never, ever find everything out. What happens is that the more research you do, the more you learn, and the more your learn, the more information there is to as more (and better) questions. As I work on how bacteria become resistant to antibiotics, if (and when) I do answer the particular set of questions I have about a particular antibiotic, I will just move on to a different antibiotic.
Like Jim said, once you’ve found something out it usually presents more questions than it’s answered. There are lots of different areas of science so there will always be something to research, some new diseases or infections, new technology that means you can look at things in different ways or more detail.