We can try as hard as we want, but there are some things we cannot do for ourselves. It is a perfect parable for God. We are all here because of one thing. For dozens of reasons, we cannot do this thing. But the final result is, we cannot.
Spiritual birth is humanly impossible.
It must come from God. He is the only one who can give us life. Indeed, the terminology of Scripture is very much like physical birth. Jesus said, you must be born again. He was very precise on this subject.