There’s no question that bad stuff happens. When a close friend or family member dies, it’s appropriate to feel grief. Similarly, good stuff happens. If you suddenly get an unexpected windfall, for example, it’s appropriate to feel stoked.
Most of the time, though, the stuff that happens isn’t dramatically positive or negative. It’s just stuff that happens. Whether you let that stuff make you happy or miserable is entirely dependent upon your beliefs.
Everybody has beliefs about what events mean to them. In most cases, however, people assume those beliefs reflect objective reality and are therefore immutable Laws of Nature.