Possibly, in some cases, because we tend to have memory problems. Depends on the nature of the reminder system though. All the automatic ones I've tried tend to pester me at awkward times no matter how carefully I try to set them up.
But the reminder feature built into the Thunderbird email client is quite intelligently designed and seems to be as good as these things get, as long as I'm using my computer on most days. Even with that I find it nags me annoyingly unless I'm always very clever about configuring the reminders. And it's not "cloud-based" so if the computer breaks I'll be lost. It's a portable program so I could keep it on a flash drive, but the flash drive could break. I did copy it to a flash drive once, but keeping the copy I don't use up to date is a pain in the butt for some reason, and it doesn't get done. Story of my life - something becomes very useful, I become dependent on it, invent a strategy to mitigate the effects of losing it, get bored with maintaining the strategy, stop bothering, then it lets me down. But so far, so good.
I suppose Google or whatever might be more unbreakable, but I don't trust Google with all that personal data. Thunderbird is private, local, and without nonsense.
I certainly benefit from constant reminders, or more accurately, from timely reminders. Constant reminders get annoyingly distracting and I stop heeding them.