The practical answer is "the time to failuer is usually shorter than the time you wanted to keep the data for".
In other words, if you don't have a strategy for making backups, start one now!
FWIW, we once had a situation at work where we changed workstation suppliers, and installed a few hundred identical workstations at the same time. Aboot 3 years later (after running 24 hours a day 365 days a year), they started dropping like flies with disk failures. After about 10% failures within a few months, we decided to replace all the disks - it was less disruptive to do that in a planned manner than fixing them one at a time as they crashed.
ANY hard drive can fail at any time--or could last for decades. If you have any information on a drive that you cannot afford to lose, be sure to copy it to another drive (and perhaps to a drive that you can store off-site as well).