The only major regret is buying a T1. Got suckered by HF hype around it, picked it up on Massdrop, still thought I paid too much for it. PoS is not neutral or transparent, it's just boring. HD800 and Stax were more detailed, HE-500, he-6, and th900 were more fun to listen to, and the gs-1000 are better for the types of music I use them with. Also, the soundstage of that set of cans is really strange, hated it. It's also really telling that I couldn't sell them for a 25% loss.

TL;DR - Hype trains suck, don't get caught up in them.

Only two buyers remorse situations:

1. Pioneer Elite PD93 CD Player (early 90's).  I got a good deal, at a dealer, but it was one problem after another.  And the local Pioneer authorized repair place seemed to be more appropriate for car stereos... I chuckle when I read comments about the unit now with people saying they don't make them like they used to.  Thank God.  Replaced that with a McIntosh MCD7009 because I swore after to only go with companies that provide great support and don't have, essentially, planned obsolesence.

Then, 20 years later...

2.  Sennheiser RS220.  Based on reviews, I thought wireless might finally be worth trying for a "TV" pair of headphones.  Average sound at best (think $50 instead of $600 headphone).  But worse, I'd been willing to try it partially based on my good experience with Senn support.  I probably used the thing less than 20 times over 2 years.  Then, it completely crapped out on me and I go to find:

I regret a great many things in audio, in chronological order:

Getting my first advice on headphones from an online retailer (Goodcans) and then spending the better part of the 00s listening to Grado headphones. SR125-->RS1-->Head-F1-->SR200 (which turned out to be the best ones).

Wait, no, I don't regret that, a lot of good albums came out in the early oughts and I'd be fucked in the head to have stuck with my Creative computer speakers and stock CD player headsets. Only real regret is that the hyped grado sound kept me from appreciating some genres and recordings/masterings.

Second regret is thoughtlessly browsing head-fi reviews and taking them at face value. The distribution of the headphones I bought was such that about one out of a dozen tended to get more headtime than the other 11 combined.

Oh yeah, I kind of regret buying a couple of dozen of low-to-mid-fi headphones. Look for people who have been in the hobby to become cynical enough not to fall into the "new toy followed by increasing bitterness and further gadget lust" cycle, or at least those who have gone through the cycle enough to accumulate some solid knowledge and experience. Then survey like a half dozen such sage beings and go for the most consistently recommended headphone, even if it is TOTL -- so long as it's not there because of platinum bling and tender goat nad earpads.

Then there's the source bullshit. At this point you're really chasing those last couple of percent and I'm of the mind that the point of decreasing returns concerns mainly functionality rather than any possibly audible improvements. Not that there's anything wrong with covering up a headphone's flaws with muddy tube amps or reduced electrical damping, but that will always lose out to an optimal pairing of mutual yet independent greatness.

And for the love of god don't worry too much about specs and measurements. My guideline is that if everything but the signal is kept out of the first 60db (at source, -40db at headphone), then you're set for most every occasion. Oh, and with that comes the lesson that people really do hear differences, but become very offended when their perception does not directly correlate to testable and measurable results. Apparently the brain is a figgity organ which despises being told that it's a sack of densely networked salt circuits tracing their way through fatty tissue rather than a goddamn microphone pre + adc. That's the hardest lesson and consequently it's the most shat upon one among headphone communities not mainly populated by Asperger'd minds which are thusly unencumbered by certain vital aspects of being human.

But that's not even the most important lesson. I've learned (and slightly regretted) fussing over gear at all. While I can appreciate aesthetic, intellectual and emotional notions of the endless modding/diying, up/sidegrading and antique ritual (vinyl, toobs, etc.), the quintessential joy of the hobby is the listening experience itself. The critical listening, when it's quiet and you're alone with your eyes closed or the lights turned out. Unfortunately we are burdened with the attendant worrying about frequency response, brickwalling, oceanic fauna and the like to the extent that it manifests as a neuroticism which keeps you from being able to fully enjoy and immerse yourself in the listening experience. So yes, you need the right headphones/speakers, source and whatever aesthetic flourishes you require, so long as you do not go overboard. Less is more.

I feel like I've been a bit lucky getting into this hobby, in that I didn't waste _too_ much money on the wrong gear.  I realize this thread is about regrets, and I purchased some gear that didn't work out, but most of the gear I bought that I didn't like was also what evolved my listening sensibilities.

So I started with vModa m100's, cuz I wanted moar bass.  I thought I was a basshead. At first I was thrilled, but it didn't take too long for me to realize that I didn't really like emphasized bass. So I learned something from that purchase. 

After that I bought several cans from Amazon, but ended up returning them all - Senn Momentum over-the-ears, then PSB M4u2s, and logitech ue6000.  So I was already discerning things and not satisfied with these, but I had the luxury of Amazon's return policy.

Then I settled on the HiFiMan he400.  My first open can.  Loved these at first. They felt fast, layered, wide soundstage, and I really liked the treble at first.  Lots of energy up there. But eventually I realized that the treble was too hot, and a bit sibilant.  And the upper mids/lower treble, where were the upper mids?  I experimented with eq and realized that bumping up the upper mids/lower treble really helped, and pulling down the 10khz helped.  So I was still pretty happy. But then I started hearing distortion all around.  It really got ugly with tracks that had a bricked up compression. But I was learning.

I came here and based on a lot of reading and advice finally pulled the trigger on hd650's. I had resisted these cuz they seemed old school and I worried about the "sennheiser veil".  But I was immediately captivated by them. Loved the rich mids, the rich tonality, the smooth yet resolving sound.  And a few months later a nice Valhalla 2, which kicked it up to a new level. I feel like I am finally onto a really nice rig.

tl;dr So this is a story of having bought some gear that I didn't end up liking, but it was also the stuff that I needed to hear to educate my ears and move up to the next step. I couldn't have appreciated things without that experience. Not many regrets.

hello,

riding a motorbike daily for three years straight without knowing the value of hearing protection. (documented trauma damage.)

buying a series of cheap ass phones for Mrs Forbin as she kept breaking them. finally learning that better build and replaceable cables are the only way to go for her use pattern.

not buying portable amps soon enough to realize their benefit when using higher impedance cans on the go.

attending local meets where my choices (all mid-fi) need to be defended to folks with way more disposable income than my household commands.

having Mrs Forbin be uncomfortable at these same gatherings as this hobby at times seems extraordinarily testosterone driven.