Having been a test lab admin for a storage company, I have seen the full depth of the hard drive bathtub curve. For 6 years, I curated a test lab with over 10,000 drives.
https://www.backblaze.com/blog/how-long-do-disk-drives-last/
For the first 3 months or so, the drive failure rate is pretty high. We used to get around 2-3% of drives fail on new projects within that time frame. (I had one project where every single 3TB SAS drive failed in the initial set within the first month. We had major backlash against that company. However, I can't mention who it was for fear of law suits.) Always keep your old drives and backups long enough to get past this initial failure time. A better bet is to keep new drives under stress testing for that initial 3 months before putting it into production use. That way you know it works before you start using it.
The second phase, between 3 months and ~5 years, the failure rate on drives is pretty low, like around 0.1-0.5% for enterprise drives, and I've heard less than 1% for consumer level drives. (I did have one brand of enterprise drives that had a failure rate of 50% per year during this time, so it does vary by brand. On that note, never buy Fujitsu brand 2.5" 15k SAS drives used. They are NOT reliable. Fujitsu sold their production line to Toshiba after that fiasco forced them out of the enterprise drive business. Even 46GB, 74GB, and 136GB 15k drives from Toshiba suffered from this issue because of bad design.) Through this period, most drives are almost completely without worry for operational status. There is a small chance of failure, but not much.
At the end of the curve, after about 5 years, drive reliability suffers badly, and gets worse and worse over time. It goes from ~1-3% failure rate at 5 years to ~10% at 6 years, and ~60% at 8 years for consumer level drives. Enterprise drives last longer, typically a 10% failure rate at 8 years, and 50% at 10 years. I advise not keeping any useful data on a drive over 6 years old, ever. There are drives that last longer than that, defying the odds, but do you really want to take the chance?
The biggest lesson here: keep redundancy and backup in mind, always. Use RAID and have nightly backups for any valuable data.