That's why people inside the stadium cried. Why folks watching at subway stations gasped. Why his personal coach was too overcome with grief to speak at a news conference.
The Olympics, however, still went on Monday, without Liu or Phelps. At least there's still Usain Bolt and his bid to become the first winner of the 100- and 200-meter races since Carl Lewis in 1984.
Bolt was second in his opening-round heat of the 200 in the morning, then easily won his quarterfinal heat at night, jogging down the stretch and still topping the reigning champ Shawn Crawford of the United States by several strides.
Other notable events included another rout by the U.S. men's basketball and softball teams, a frustrating silver for gymnast Nastia Liukin and a bad break, in more ways than one, for U.S. cyclists.
The United States still tops the medals table, now with 72, but China continues to run away with the most golds. With four more Monday, the Chinese are up to 39 (more than the overall count for any country but the U.S.), while the Americans have 22.
Also, Britain is up to 12 gold medals, its most since 1920, and kudos to male long jumper Irving Saladino for picking up Panama's first-ever gold in any sport.
Track and field
The U.S. flag finally rose at the Bird's Nest, and it came from an unexpected source when Stephanie Brown Trafton won the women's discus. It went up again later when Angelo Taylor won the 400-meter hurdles, with Americans Kerron Clement and Bershawn Jackson taking silver and bronze.
After capturing only one of six possible medals in the men's and women's 100, watching the 1,500-meter team of Bernard Lagat, Lopez Lomong and Leo Manzano all fail to advance past the semifinals, and seeing Terrence Trammell get hurt in the opening heat of the 110 hurdles, Brown Trafton's victory was a much-needed lift. The 400 sweep was awfully nice, too, something no country had done since the U.S. in 1960.
Also, Russia's Yelena Isinbayeva won her second consecutive gold in women's pole vault, topping American rival Jenn Stuczynski and then upping her own world record to 16 feet, 6 3/4 inches; Brimin Kipruto made it seven straight Olympics that Kenyans have won the men's 3,000-meter steeplechase; and 18-year-old Pamela Jelimo led a 1-2 Kenya finish in the women's 800.
Despite the pain of a lingering hamstring problem and the added bother of a tendon flare-up in his right foot, national pride carried Liu to the start line.
He took off at the gun, took three strides and then began hopping on his left leg, the good one. Someone else false-started, so he could have tried again, but there was no way. He peeled the lane-assignment number off each leg and headed for a tunnel.
"He couldn't imagine the pain he was suffering," said China's track and field coach, Feng Shuyong. "Let me repeat: Liu Xiang will not withdraw unless the pain is unbearable."
So the guy who croons in a music video, appears in TV commercials and looms on billboards will no longer have his gold-medal defense play out daily Monday through Thursday.
"After Liu Xiang's injury, I won't bother coming back to the Bird's Nest for more," a 67-year-old Chinese fan said as he left the stadium.
It's a good thing Nastia Liukin already won the all-around, because the way she got silver in the uneven bars is enough to drive a gal nuts.
Liukin and China's He Kexin got the same score, requiring a tiebreaker because dual medals are no longer awarded in gymnastics. The details are pretty crazy; all that matters is He won and Liukin didn't. He, by the way, is among the girls who many believe is too young to be eligible for these games.
This was Liukin's fourth medal of the games, matching her dad's haul when he competed for the Soviet Union. Coincidentally, one of Valeri Liukin's golds, on high bar in 1988, came in a tie.
Oddly, there also was a deadlock for the men's vault gold, which went to Poland's Leszek Blanik.
Chen Yibing extended China's perfect run of gold by winning the still rings competition. That string ended only because no Chinese men qualified for vault.