Many have made the same mistake, myself included. As you say, greed is one of the main mistakes in our life. I came to the conclusion that if you have already made a profit, you should not return to this, but it is better to forget and move on.
I think almost all of us experience this kind of mistake. I also has an altcoin that were once less than a dollar. I got around 3k+ of it and the token was pumped to $19+ I failed to sell it thinking that it will surge more. So I keep on holding the token until I realized it was too late to sell because the token become worthless.
I'm sad to hear that. One thing you should avoid, do not buy tokens in large quantities when the tokens are still in the Launchpad (ICO) stage. Because some Investors believe that Launchpad will give them a return on their investment.
There are instances when a token on launchpad gives profit to investors, so many investors try their luck and invest during the initial stage of coin selling. But we must make sure that we had done our research before investing in these kinds of projects.
Second, if you have sold tokens and then get a profit, I don't think you should buy again when the price is still high. So, just stop there.
True, we must not FOMO after we sell at a profit. Often times investors got burn when they buy back during the price surge. We should wait for the right time such as correction and price drop and make sure that the project developer will not abandon the project.