The number one reason not to invest in crypto is the risk that every crypto have, investors always fight and accept every consequences once they invest in an altcoin, two possible things will only happen, success and lost.
Actually, it is not only in cryptoinvestment whereas risk is present but to any kind of investment. Risk is due to the sudden changes on the market value of every crypto which is a bit of a downside for an investment. Unlike in real estate or stocks that most of their price is stable, cryptos' market value are not. But if only investors wouls be commited and patoent, there's nothing to be worried of because dumps are not permanent.
Moreover if someone is destined to meet failure, he will come across it one way or the other. Ups and downs are part of human life. We cannot run away from them. Success is not a destination but it is a journey and many people do not even start that journey so they do not get what they desire for. Crypto currencies are a big chance to make dreams true.