I am also one of those who brought bitcoins early but also did sell my coins thinking I have made enough profit off of bitcoin and now I am regretting my decision, so what else to do now?? That's the reason why I keep on investing in altcoins and hoping that one day I would potentially hit a gold mine and would redeem the mistake I did with bitcoin. But till now I am still unlucky and not found that project that would make me a millionaire, so the hustle must go on. Another reason would be that altcoins are now being more innovative than that of bitcoin, bitcoin is still the same as it was from the start but it is not the same with altcoins as they are providing more value to cryptocurrency economy and day to day use.