system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is Quantum physics considered "scary" to people who understand it?
gpt
It's scary to the following groups of people:

- Much of the physics community from when it was first being discovered.  All of science depends on experiments being reproduceable.  Things will happen the exact same way in response to the exact same stimulus every time.  Discovering the way things work and defining it mathematically allows us to do phenomenal things, like build skyscrapers and be sure they won't collapse under the load.  Quantum physics seems to defy this, quantum-level events happen according to probability, rather than being deterministic.  If quantum rules applies to macro-level physics, a lot of what we understand about the world would be useless.  Fortunately, this turned out not to be the case, and few people would take this fear seriously anymore.

- Science Fiction writers.

- Philosophers discussing the existence of free will.

- Students who don't actually understand Quantum physics, and are afraid of the next test.