If there's one thing computers do well, it's malfunction. Plan ahead so you don't lose data should your Mac start behaving more like a computer.
Last month, while download Mojave patches for at least two zero-day exploits a malfunction occurred and I couldn’t upgrade, leaving my machine vulnerable:
During a 10 minute chat with Apple Care it was suggested I back-up and restore Mojave. The resolution wasn’t exactly what I’d hoped for. But not a big deal as I hadn’t created a backup in 3 years and it was about that time.