For me there are 2 types of "regrets".
The easy one: Watches I sold for market price at the time (or less
) and now require stupid money. No real regrets here, for investment the stock market is my friend.,
The 2nd one, and that's not easy, is watches I sold that I just can't replace. usually rare variants and a super rare good condition. Finding good examples of vintage these days is just impossible (or ridiculous amount, but with all the Frankenstein watches, even if I'd like to spend, I won't trust the genuinity of the watch),
The number one regret is an unpolished, untouched, in genuine original condition, full set/provenance 1675 Tiffany dial in NOS condition from its 1st owner.
But then, I recall why I sold them, they were too precious in condition to wear (I do wear my watches).
So, here's one to match your photo, oldie but Goldie...