invest only what you can afford to lose
This is very true; safe in bitcoin is subjective and it depends on the person on how much they know about investing in Bitcoin. Once they are ready and they have planned well about it, I guess it's time to start investing. You need to be aware that is really risky to be involved in the investing alone, and we're talking about bitcoin. Given that the price is kinda high, we should not be complacent about it.