In other words, invest only what you can afford to lose.
To sum it up--"Buy when the price is low and sell when the price is high, BUT invest only what you can afford to lose."
It may not guarantee a profit but it can help cut down loss when the bear attacks.
I wish the folks that got burned in the UST/Luna fiasco would have perhaps waited for a moment and accessed the risk of what they were doing by following your advice. I'd also add -- the price charts don't have to show immediate volatility in order for there to be an incurred risk that's disproportional to any potential gains. You could be sitting on a bubble that's been stable in it's inflation until an immediate pop sends the market tumbling. Generally there are signs when growth is unstainable, but it's not always in the numbers. Need to use your head sometimes.