Hard disk drives go on sale regularly. I replace mine usually once a year or so. They're not expensive relative to the loss of the data. I just bought a 500G SSD drive on sale for $60.
- Solid-state media...store data using electrical charges, which can slowly leak away due to imperfect insulation.
- Magnetic media...may experience data decay as bits lose their magnetic orientation. Periodic refreshing by rewriting the data can alleviate this problem. In warm/humid conditions these media, especially those poorly protected against ambient air, are prone to the physical decomposition of the storage medium.
In either case, only ZFS/Btrfs/ReFS seem to implement strategies to deal with data corruption. Kinda sad that Apple recently released a new FS and didn't bother to address this.
It's not stupid but redundancy is important, don't rely on cloud only.
My own anecdata: I lost a couple TBs with Streamload[0] ~2007 when they switched over to MediaMax. They wouldn't admit it was their fault and I never got any kind of compensation - even though I had just renewed my yearly subscription a couple months prior. Thankfully I had offline backups on CD/DVD but that was definitely no fun. More recently CrashPlan decided to no longer offer unlimited backup for non-enterprise users i.e. I would have to pay a LOT more money to back up multiple TBs. At least they offered me a partial refund for the remaining months in my yearly subscription. I really really hope Backblaze keeps their unlimited plan.
As for physical backups, my 8-drive RAID-5 GPT partition got somehow nuked when I was trying out a new Windows 8 installation (one of the first official builds). I never found out what actually caused it, but I immediately went back to Windows 7 and waited for 10 to be out for a couple years before finally switching over. I'm still paranoid and keep my backup server separate and off the network except to make diff backups.
Bit-rot is also becoming a serious issue. I hope to finally build a home ZFS server (with ECC RAM of course) to deal with this, as I've noticed non-streaming encoded videos sometimes just stop working after 15+ years. I'm not sure if it's actually bit-rot but I can't think of anything else that would cause this to happen.
In any case, keep multiple backups: offline and online!
[0] https://en.wikipedia.org/wiki/Nirvanix