I regret leaving bitcoin; last time 1Bitcoin cost like $600 now look where it is now; i would've made a really good investment. I only had like 0.5Btc in my account; im glad it gained value but i know i could've earned so much more if i stayed.
You are not too late for start again, I know the bitcoin about 19 months ago when the price no more than $200. Then I bought 5 btc and I sell when the price reach $560 in may 2016, by that time I had no idea there was a halving day because I thought it was lucky, after I sell all stock, I leave and active again 4 months.