For me the most depressing thing has been - once I've seen the OTP library and everything elixir (well, erlang) provides, I've realized we've figured out most of the things like 30 years ago and have kept reinventing the wheel constantly, just because of not looking back and checking has it been solved already. Erlang's introspection tooling is better than 99% of what the market offers now as an expensive SaaS.