I don't know any programming context immune to human errors. Stuff just breaks. Sometimes I get lucky and the guy before me wrote a cool test that prevents me

I don't know any programming context immune to human errors. Stuff just breaks. Sometimes I get lucky and the guy before me wrote a cool test that prevents me from having to start a debugger, but the contrary is often the reality. OSS stuff is usually better, but not much better (OS upgrades always break, for example).