Not buying some the first time I became aware of it in the $10s. It seemed too hard to purchase back then...it would have been worth the effort.
In 2015 I shamelessly turned down an opportunity to buy around
BTC5 at a very cheap price. This happened as I had my doubts about it's future exploits and I had lost a huge sum to trending ponzi schemes making the waves at that time. When I realised I should have invested in it the price became outrageous. Since then I always do my due diligence and ensure not to pass another opportunity to grow.