It's easy to believe that there's always a higher peak — there's always another upgrade to lust after, and possibly save up for and actually buy. That first time you listen to something new is always (or, at least, usually) such a memorable, significant experience that it's tempting to recreate it. But, of course, you can never match the feeling of hearing [equipment X] for the first time.
Once you're accustomed to amazing quality, it becomes normal to you. That doesn't mean you stop caring about quality — it just means that you've succeeded in reaching or approximating "the best", whatever that means for you.
After that point, it's easy to look around and think, "What else can I upgrade? What's the next level? I just spent $1000 on headphones, so this $200 amp must be insufficient. A more advanced DAC was just released, so I'm not hearing the best quality that I could be hearing. There are $400 cables out there — surely there must be a noticeable difference over my $5 set. And I'm still using this inferior stock power cable, plugged into a consumer-grade, unfiltered surge strip!"
Someone will always be happy to sell you another upgrade, and you'll always find people who tell you they got it and heard a huge difference. But most of that is placebo, and the few upgrades with real benefits might be measurable but not necessarily noticeable.
Once you reach the point in your setup where you're struggling to hear the difference with an upgrade, there's no shame — and plenty of sensibility — in pausing the upgrade train (I won't say stopping — let's be honest with ourselves) until there's something better out there that you'll actually get a major, noticeable benefit from.
A sequel to your favorite headphones? Worth investigating.
An entirely new kind of headphone, or a new generation of old tech, that has the community raving? Worth investigating.
Everything else? Rarely worth the time or money.
I've seen so many people get a nice midrange set of $300–500 headphones — say, the HD 650 or DT-880 — and then spend $2000 over the next couple of years on higher-end supporting equipment than they (or anyone) can really distinguish, while they could have instead just spent the same (or less!) on, say, an HD 800 and an Asgard 2, fed from a Mac or iPhone's built-in (and surprisingly good) DAC. Few people, even around here, could honestly say that the midrange headphones with the fancier amp and DAC would sound better overall than the flagship headphone setup with the "value" amp at a similar total price.
Recognizing this doesn't mean you're losing interest — it means you're realizing what matters to you, and what doesn't.