It's having a weapon that you can practice with for years AND carry without wondering if your trigger spring is finally going to fail in the one gun fight of your entire life.
But that's always a possibility. I do survival analysis, or at least I used to, for different companies. Even a Glock, which whatever folks say about them are documented with very high round counts, can have a faulty trigger spring that could snap at say the 1000 rd mark. Is it likely? Very much not. Is it still possible? Yes. It might not even be a design issue, but simply a bad batch of parts or a bad install at the factory. Now sometimes extensive testing of a large number of pistols will reveal tendencies, such as broken trigger springs. But it takes more than one example posted on an internet forum to derive a trend. For that what we really want to see is large scale agency adoption and then reports of how those pistols did after a number of years (because it gives us a large sample size and harder use than we might see from some civilians, exceptions apply of course). Unfortunately, manufacturers aren't exactly keen on such information getting out, so even if it were an issue the only way to find out about it would be a manufacturer issued recall or the second hand story from someone in that department.
Also, what failures are we looking for? Are we looking for catastrophic failures of slides, barrels, or frames? Or are we looking at the annoying trigger spring that can turn a $550 pistol into a paperweight? Now even if those did fail, is it a sign of a trend, or did the owner not replace the part in question at the manufacturer recommended interval? Some guns have crazy replacement schedules where you almost never need to do anything to them. Others are much more regular.
I'm not trying to dismiss your comment, or the OP's concerns. They're valid concerns. My only comments are that it's very hard to get info on this. Now we do the best we can and ask around, just be aware that if I only poll early Gen 4 Glock owners they might have a lot of negatives to say, where if I polled current Gen 4 Glock owners they might be relatively happy. Get as much info as you can, and resist the temptation to go with one very positive report.
P.S. - I bring up the money not to dismiss the idea of high round counts, but just remind folks how much an investment shooting can be and to consider if that's an investment likely for him/her. I could buy the absolute most durable AR on the market, but am I okay with the AR that will last 30,000 rds when I will only ever shoot 2,000? And what if the money I will save will allow me to shoot much more and be more proficient? For the lucky this isn't a concern and they can get the best in all categories as they have the coin, but some aren't that lucky. Just food for thought.