In 5 years of running 3x Dell R620s 24/7 - which were already 9 years old when I got them - I had two sticks of RAM have ECC errors, and one PSU fail. The RAM technically didn’t have to be replaced, but I chose to. The PSU of course had a hot spare, so the system switched over and informed me without issue.

IME, hardware is much more reliable than people think.