There are big waves, very big waves, and seriously dangerous waves. The trick is to know when to stop.
Time to wave goodbye?
The problem with mountain climbing is: what do you do once you've conquered Everest? Garrett McNamara has faced no such difficulty in his chosen sport. Having tamed the biggest wave anybody had ever surfed, he's gone out and found a bigger one.
McNamara, 44, from Hawaii, hit the headlines last year when it was confirmed that the breaker he rode off the coast of Nazaré, Portugal in November, 2011, was a record-breaking 78 feet (almost 24 metres) tall. Now it seems he's gone one better, with video released on the internet of him tackling a monster wave in the same waters. Some pundits say it could have been as big as 100 feet.
After his previous attempt, the surfer told The Observer newspaper that he has the support of the Nazaré government, and he is helping officials there to discover more about a 1,000-foot-deep underwater tunnel that "acts like an amplifier" when there is a big ocean swell.
If this latest ride is recognised as a new record, what's next? McNamara has said that waves in the area can rise as high as 300 feet - but "you can't contemplate coming off because it would kill you".
Gnarly effort dude, but having twice defied the odds, maybe it's time to quit before you fall off the mountain.