Computers fail, eventually.
There are hardware failures, and software failures.
Hardware is nice, and tends to fail one part at a time. So, if your system breaks, you can replace the part, and be operational again.
That's assuming that you can still purchase the part. You may have a spare, but, does it still work? Some components, like electrolytic capacitors, can age and fail.
Software failures are harder to detect, and sometimes, software failures are invisible when they happen, but manifest symptoms later, with bad data being revealed.