We have to avoid being blamed because of their losses and because of their mistakes. Let them understand that before investing they also know the possible results and difficulties to encounter in order for them to decide or just forget it.
As this market is full of uncertainty, it is indeed hard to advise someone to invest on this market. Good if someone is willing to listen, but you need to make sure that he knows the consequences of getting into this market. Because you can't assure that his strategy will work or not, depending on the coin that he's about to get involved with. If they are serious about investing on this market, they will also dig facts on their own, and study the market.