HDDs have high failure rates; all the brands release defective units, batches, and models. Corporations use equipment that mitigate failures through intelligent software and by allowing techs to physically hot-swap failing HDDs, etc.
As a consumer, what you can do is find reliable, middle-of-the-road HDDs that have been around for a while and are not excoriated in forums (not too fast and not too big).
Also, many (most) consumer grade external cases are rubbish. Cheap power supplies and heat are rapid failure points. But there are plenty of others. I had several consumer cases fail in a few days of limited use.
As @MHirsch noted, some RAID system is a good bet for local storage as you can mitigate HDD failure. That requires enclosure investment.
But, whilst considering backup solutions you might also consider the location domain (e.g. periodic off-site backup via the cloud or just physically moving a HDD to a different location for theft, fire, electrical spike, etc. protection).
Disclosure - me and family worked for enterprise storage firms.