Perhaps you’ve encountered a sink with two taps, not one. One for hot, one for cold, without a chance to mix them before you scald or chill yourself.
It seems absurd that the folks who figured out the technology to build sinks with running water couldn’t be bothered with the last step of making it useful.
But this isn’t the case. Centuries ago, the hot water in a home was suspect. It might have been in a unclean cistern for a while, it might carry disease–you didn’t want to mix it with the clean water unintentionally.
Now that we’ve mostly nailed the sanitary conditions of hot water, the design is obsolete. But it persists, because systems and style and culture allow it to.
We’re surrounded by obsolete design. It’s worth asking “what’s it for?” and consider what it used to be for.
Once it’s obsolete, good design becomes bad design.