I invested in Polkadot and already earned 50%

congratulations, but have you sold your Polkadot yet? Because now the price of Polkadot has risen even higher, but if you haven't sold your Polkadot then you better still HOLD, because I believe the price of Polkadot can still increase even higher, so my advice is if you want to sell your Polkadot, then you better not sell 100% Polkadot that you have, because the price of Polkadot can still increase very high and give you a bigger profit.
So he should hold because you “think” the price will go up? Please elaborate on why you think it will go up. What a dumpster post.
because Polkadot ROI is only around 500%, so Polkadot ROI can still increase again (almost all altcoin that are in the top 10 on coinmarketcap, have an ROI of more than 1000%), besides that the market has not yet had a bull run, but Polkadot price has increased very high, so if an incident like January 2018 occurs again (bull run), then of course the price of Polkadot will increase even higher than the current price and can even make new ATH price again.