Beware of betting on horses.

Consider the two men called Ma (“horse” in Chinese) – Pony Ma Huateng and Jack Ma Yun, who have dominated China’s new economy space for years.

Both Tencent Holdings in Hong Kong and Alibaba Group in the United States have suffered huge sell-offs, with investors dumping their darlings in the wake of investment uncertainties.

Tencent was apparently hurt more than Alibaba Group, just as Hong Kong equity has trailed the performance of that in the United States.

Tencent fell about 40% from its peak of HK$475.72 (US$68.7) in January this year to close at HK$286.4 on Wednesday, wiping out HK$1.8 trillion of market capitalization. The company is now capitalized at around HK$2.73 trillion (US$348.34 billion).

By comparison, Alibaba Group also lost close to 30% from its peak. At US$149.21, Alibaba lost HK$1.26 trillion in market value.

In other words, the two Mas lost a combined HK$3 trillion in market cap, or the equivalent of an Alibaba, from its peak this year.

Tencent has now dropped out from the world’s top 10 companies despite 21 consecutive days of shares buybacks.

As a result, chairman Pony Ma, who owns 8.6% of the company, has seen the face value of his personal stake drop nearly HK$150 billion.

Ditto for Alibaba Group’s Jack Ma, who plans to retire next September and has designated five unnamed parties to succeed his ownership in his variable entities.

The sell-off in the two Internet giants reflected a re-examination of how these companies earnings will fare in the wake of huge capital expenditures and in times of increased regulatory control of their businesses.

Beijing stepped up its regulation over the impact of social media on teenagers.

Tencent, the largest online game operator, was hurt by Beijing’s repeated efforts to set time limits for teenagers playing its banner game “King of glory”.

And just yesterday, Beijing also initiated a ban on users below the age of 14 from using Weibo, Alibaba Group’s Twitter-like messaging system.