I usually use an old adage that was also repeated by Louis Rossmann: if a piece of data is not stored in three different places, it is considered lost.
I can't afford to have complete separation of places (at home, in the cloud and at a bank safe), but I leave copies in three different places - one of them is a four 3TB HDD RAID5.
Unfortunately the amount of significant data took a steep turn up (kids were born, then youtube channel) and therefore optical media did not cut anymore, leaving me only with HDD as a feasible solution.
That said, I have 25+ years old CDs recorded in 1x, 2x and 4x that have zero error till this day. I also happen to have a SCSI-2 80MB HDD that still works and has no more errors than its error table. Quite amazing, especially due to the doomsday scenarios of the 1990s regarding magnetic and optical media degradation. Streamer tapes were a disaster for us (1990s 120/250MB), the Iomega solutions were quite good (I was lucky) and I lost count of how many flash drives and pendrives I lost. With this, I still keep all that data on HDDs.