Q: If quantum mechanics says everything is random, then how can it also be the most accurate theory ever?
Physicist: Whether a quantum system is random or not kinda depends on what you’re taking about. For example, when a beam of light passes through a beam splitter the beam splits (hence the name) into two beams of half the intensity. The quantumy description of each photon going through the beam splitter isn’t a simple as “it’s totally random which path it takes”. Take the same situation, a laser going through a beam splitter, and add a little more to the apparatus. The non-randomness of quantum mechanics is the basis of quantum algorithms, and (in a less direct way) is why chemistry “works”.