If you think that’s transitory, have you seen FaceBook? Twitter? If it’s not from like this week or newer, it’s effectively gone forever, impossible to find again.
I dare people to try to find article they saw on Reddit a week ago. It's pretty much impossible. The built-in search feature is worse than useless and even Google's index struggles unless you remember the title exactly, and even then it can be a crapshoot.
Reddit's search is more useful than is generally given credit for, though it's not spectacular.
Searching link submissions on Reddit is all but impossible, given that the search targets are typically just the link title itself. If you have a given URL and you want to see if there was any Reddit discussion, you'll have far better luck. (Use the "url:<urlspec>" syntax).
For self posts (that is, original content submitted to Reddit as text), the likelihood of a hit is far larger as there's much more text to search off of.
Even better: you can restrict search by the date-range presets, or if you don't mind submitting Unix timestamps, any arbitrary date specification in a signed 32-bit range. You can also restrict search by subreddit or submitter, among other criteria.
I've made ... reasonably good use of Reddit as an essay repository with the ability to recall any of somewhat over 500 items over the past decade or so, posted to a personal subreddit. It helps of course that I usually have some idea of the language I'd use, and/or repeat myself a lot.
There are limitations. Reddit doesn't index comments, and searching large subreddits or globally is now quite difficult due to the sheer volume of submissions. I wouldn't say Reddit's search is great, but used with intention, it's serviceable.
(The rest of the site is ... failing spectacularly to serve my needs, I'm not endorsing it at all. But search actually does provide utility.)
These days I find HN an even more useful personal pattern repository, thanks to Algolia and the "by:<username>" filter.
I can usually get pretty close even months later but some things escape. It can be frustrating to spend a long time trying to find an article you forgot about and then not finding it.
If I can remember part of the title, I always put that in quotes and if I see something I know it's not I use the term exclusion feature.
Sure, and the Internet Archive has the Wayback Machine. But these are not commonly known and used tools, so for normal people, everything is a constant now, and whatever is yesterday is forgotten.