Cellars are continuing stories until the end, either eternal, or until the liver or feeding tube gives out. Sure, there are things I wish I had allocated better, perhaps not bought too much of, but overall, it's like Frank Sinatra: "regrets, I've had a few, but too few to mention."
Unlike some here, my focus has been broad, but mostly European, and I try to go for wines that age well for over a decade, so I try to keep 'current' drinking wines to a minimum since I may not get around to them in time. And I seldom purchase in case quantities ( I think the last time I did was for Huet in 2002), because there is just so, so much wine flowing out there that it's hard to ever feel regret when that last bottle flows.
In some ways, the building-a-cellar philosophy is as endearing as the home built by a person instead of a commercial homebuilder: you live, you learn, and sure, maybe the windows could have been placed better, the patio enclosed, etc., but it is something you did, and reflects the idiosyncracies of the person behind it.