Everything is hard until it's not. Invisible electromagnetic waves are invisible (hard) and frequently deadly (hard!), but now we have WiFi, cell phones, GPS, xrays, etc.

Superconductivity is absurd magic and took impossibly low temperatures until they weren't impossible, and now it's driving MRIs, massively improving medical research, and the realm of usability is constantly expanding. Absolute zero was known reasonably accurately for over 100 years before liquid helium was achieved, and superconductivity came only three years after.

It's the kind of thing you can frequently only judge accurately in retrospect.