I've had a bit of luck of late - everything I have on HDD has kept going without issue. However, I did have a 2 year period when I had a total of 5 HDD failures. One was a Western Digital enterprise level drive that lasted a total of 12 days - warranted for 5 years! It would only have had about 10 continuous hours in use.
Why is this relevant to you?
HDDs are so cheap these day that you'd be NUTS not to buy a Synology DS that can do RAID 1 and run two drives in that configuration. If you have a single drive and the drive fails, you'd better have everything backed up. At least with RAID 1 (mirrored redundant array) you can have one of the two drives fail and lose nothing immediately, although that's no excuse not to have a full backup. These days drives are huge things - think of the pictures/video/music/whatever you store on one. 1Tb is a HUGE pile of stuff to lose if you lose it.
ALL HDDs can fail. None of them are guaranteed not to fail. They are all cheap and have to be made to a price, so failures are just part of ownership. Just my thoughts...

