@hyeyoo Have you watched Ben Eater's videos on YT, where he builds a CPU on breadboards?
If you follow his videos from the start, a lot of concepts that you've heard about but don't currently get will click.
At least they did for me.
@hyeyoo Stop thinking about digital signals as those beautiful rectangles on paper. Imagine what they really are—large amounts of electrons moving by laws of quantum mechanics. Then it becomes clear that everything is just a matter of probability, and it's a miracle that electronics works at all.
@hyeyoo Then again, if you take enough electrons in an electric field, their OVERALL movement follows some more sane rules. But some electrons will still “refuse to behave”, moving in other unpredictable ways and creating noise.
More importantly, unless you're in a well-shielded lab, there are those external factors affecting the above-mentioned electric field (EMI), microscopic material defects, cosmic rays and whatnot…
@hyeyoo As everything in this world, it's a matter of probability. Tell me how low probability of failure is considered safe and then I can give an answer!