What are your Eureka Moments in this Hobby?

I was switching back and forth between my solid state Hegel H200 and my tube CR Developments Romulus Integrateds depending on my mood. Then one day, Eureka!!! The H200 has a Theater Bypass channel and the Romulus has a Preamp out!!! Connected the Romulus to the Hegel and WOW!!!!!! 

The first time I decided to spend $1000 on a MC Cartridge.  Everything changed.

Nice @maprik  and  ​​​​@maam522a  !

I recently found a pair of interconnects (directional) installed backwards.  Not quite ‘eureka’ but maybe ‘duh’!

1 - Replacing my CDP with separates (CD transport and standalone DAC).  CDs are my primary listening medium and this was a significant improvement both sonically and from a future upgrade standpoint. I have since upgraded both my CD transport and DAC since making this initial change.  I am also able to use my standalone DAC with my streamer and bypassing its inferior sounding DAC.  For these reasons, I would never go back to all in one CD player.

2 - Adding a pair of subwoofers to my stand mount speakers. For about 1/10th the cost of my speakers, the subs not only improved the bass but also the overall sound as it allowed my speakers to work more efficiently. I also purchased from a local dealer who helped with placement and set up free of charge.

Most people here are talking about equipment, but my moment is simple: implementing the Sumiko Master Set speaker placement method. In a word - revelatory.