or on macOS, although I'm not sure it's still by default using case sensitive file system or not. I do remember the first time that bit me though, being a programmer using Linux collaborating with a developer using macOS. Must have been in ~2005 or something.
The one which bit me happened when I was running a java minimizer / obfuscator on a Windows platform and it assumed that A.class was not the same as a.class. It worked great on Linux and didn't warn that it had overwritten a file, resulting in a package which almost worked.