Generally speaking, interfacing with users is the hardest part of almost any program. Even when writing simple CLI tools, 80-90% of the code is often UI-related

Generally speaking, interfacing with users is the hardest part of almost any program. Even when writing simple CLI tools, 80-90% of the code is often UI-related, even though it barely qualifies as an 'interface'. Flags, documentation, sanitization, reasonable error messages, type-checking and sanity-checking the inputs...and then, generally, a handful of lines of actual, useful code.