What went up and up and up in Chinese stocks came down this week

Chinese stocks have been on a tear for months. They rose in the mainland. They rose in Hong Kong. They rose in spite of—thanks to?—a huge wave of amateur investors piling into the market. They rose despite a slowing economy and mountains of debt in margin accounts and corporate balance sheets all over the country.

Then they fell hard and fast, losing 8% between Monday and Thursday this week. But come Friday, the Shanghai Composite bounced part of the way back. If this is a bubble, it’s proving hard to pop.