If your response to the question "When did you last back up?" is something to do with parking your car, then you should really take note of World Back Up Day.
Everybody should have a contingency plan for hard drives melting / exploding / needing a bit of a lie down, and the linked website will give you lots of good advice where making sure you don't lose your data is concerned.
For many people, backing up only crosses their mind once all of their data is already lost. With the ever present threat of Ransomware lurking in the background, it's never been easier to lose access to valuable photos, videos and documents - and that's before we take into account the fact that PCs have a habit of keeling over even without Malware involvement.
According to the World Back Up Day statistics:
* 30% of people have never backed up their data.
* 113 phones are stolen / lost every minute (Ouch. You may want to invest in some remote wipe technology too).
* 29% of data deletion disasters are caused by accident.
Not great, really. I've seen everything from a workstation catch fire and 8GB of someone's files on a desktop (as in, their actual desktop with the nice Windows logo on it) vanish into thin air, to smartphones dropped in cups of tea (a container filled with rice really does work in this situation. The flaming desktop, not so much).
Throw in flood and theft and all of a sudden, you have an awful lot to worry about. External hard drives are always coming down in price, and even a pocket-sized 500GB model could be the difference between "No biggie" and "Does anybody have Houdini on speed dial?"
If you're reading this from a tablet because your Windows desktop has chosen this exact moment to never work again, never fear - the data is likely still there. There's a wide selection of emergency boot discs to choose from, which will allow you to recover your files. You can always try to repair the OS installation afterwards, but for most people the photos and files are the thing.
As for hard drive reliability in general, you may wish to check out a recent test performed by Backblaze. Note that those drives were put under extreme load - you probably won't experience that level of wear and tear during regular desktop use.
You can also check out the performance of some portable hard drives in this roundup to give you an idea of what's on offer. It's definitely worth setting aside some time to organise all of your files and start making (regular) copies - consider how much effort it'll take to back up your files versus how much time you'll lose trying to recover them all.
There's only one sensible option available...