"on time of crisis there are those who cry and there are those who sell handkerchiefs"

Now that I'm using my imagination on you speaking Spanish to me lol. I love how you put it, Chinese old saying goes, 有危机就会有转机. As in "For any crisis, there will be a turning point". And turning point meaning of doing the opposite to be prosper.

When everybody is selling, we'll be waiting at the bottom to buy them back.