Ask HN: How do hackers hack?

How do hackers hack into systems and networks, like how do they discover vulnerabilities. Is it possible to learn this? Can you guys share some examples. I have briefly read through a few hacking for dummies type of books, but non of those techniques would actualy work in real life. In the news you see so many of headlines claiming hackers hacked into bla bla. But it has always confused me of how they acctual do it. It would be awesome if you guys can share your thoughts.