They shoulda said that more gooder

Even excluding cosmic rays and other random bit flips, it's still not just "you" unless you designed the whole thing starting with sand and copper (and high quality only, none of this Ea-Nasir stuff) and wrote all the software starting from machine code.

Really what a computer does is the composition of what's it's told to do by you, the devs of the app you're using, the devs of the compiler that compiled the app, the devs of OS that compiler ran on..., the devs of the OS the app is running on, the devs of the compiler of that OS, the devs of the OS that OS compiler ran on..., ...The UEFI devs (and their compilers, etc.), the motherboard manufacturer and their design software..., the RAM manufacturer..., the CPU designer..., GPU..., etc.

That's not true there is stuff like race conditions, galactic which energy beams, broken cpus, computational bit flips, ram bit flips and stuff like row hammer, just as an example list, where the computer is very likely to not do what you said and not do what you meant

Edit: depending what you do even https://en.wikipedia.org/wiki/Machine_epsilon could be a problem

Except when I use them. Then there are error messages for the error messages that no one has seen before because I tried to print something.