is a hard drive a predictable backup solution?

I know it can fail, but if I just copy stuff on it and let it in a safe for let say 20 years, will the data still be there or will it fades away ?
Well ok I get an answer telling me that only magnetic media fade over time… well isnt the tape backup the most reliable solution available? (it is)

No, Today’s hard drives are subject to magnetic fade. This is because they use a small magnetic charge to store information on a metallic disk, and we live on a planet with a floating magnetic field. So over time you data will fade from the disks if it is magnetic charge is not refreshed. You do this by scanning the HD looking for bad sectors, copies the data & rewrites it basically renewing the magnetic charge. The basic life span of stored magnetic data is a little over a year after that it will degrade.