The most profitable bitcoins I ever mined, were the ones I mined when it was unprofitable to do so.
Yup. Bitcoin back then was unheard of by many people until the ath back in 2013. Most people jumped into the train thinking that they could get some easy money out of bitcoin. But look at those who invested during that time. They are now worrying because of the massive price drop.
And again, (I like this line a lot):
The most profitable bitcoins I ever mined, were the ones I mined when it was unprofitable to do so.