What are your Eureka Moments in this Hobby?

Back in the 1990s, a salesman talked me into buying branded interconnect to replace the cheapo giveaway cables that came with my old midfi gear.  Up till then, I was not a believer in cabling makes a difference.  But when I heard the improvement, I was astounded and went on a cable upgrade cycle, not stopping until I got all silver connects.

I have had so many, especially in the digital space. But commenting because I had the same eureka moment when I plugged in my new to me Audionet G2 and AMP1, their gear is phenomenal. 

25 years in, the list has been resorted & modified many times over. I'll try to boil it down to the big ones:

1. Hearing a Tannoy dual-concentric speaker for the 1st time at Audio Atlanta (now long gone). It was just the modest Eyris DC3 model, but blew me away with the coherence and imaging versus more conventional driver arrangements. I've been exclusively Tannoy speaker'd for years now with no inclinations to change. 
2. My first vinyl setup (SOTA Star III w/ Benz Glider). Spanked the Meridian G08 and Sony SCD-1 I had at the time. Game over for digital here, for years. Vinyl still dominates as my primary source today. 
3. Hearing my first Koetsu cartridge - a well worn vintage Onyx. The king of romantic, fun MC sound and a polar opposite to the modern high-tech Ortofon MCs I was using at the time. I thought Koetsus were stupid (pricing, several models differing by nothing but stone body) before this. Never thought that again, and started a collection.
4. Hearing Stax SR-009 electrostatic headphones on a very high end DIY T2 amplifier. Next-level headphone sound. Converted me to e-stats (for headphones). Dynamic and planar driver headphones have had a rough time with me ever since. 

Fun topic! Thanks to OP for starting.

Getting an Audio Research LS2MKII with a Bugle Boy 6DJ8, in 1998. Opened my ears/mind to both tube-based equipment and Audio Research products. Since, everything I have purchased, except one-oye, and have really happy with, until upgrade-itis, has been ARC, and has synergy with ARC.

Becoming satisfied with what I have.