Human life seems fragile at times – people have been killed by seemingly innocuous objects, like bales of hay, lava lamps, beach umbrellas, and cans of whipped cream.

But many people have tested the boundaries of human ability and resilience – some intentional, some accidental – and lived to tell their stories.

You likely have heard that generally speaking, humans can survive three minutes without air, three days without water, and three weeks without food (the "rule of threes").

Actual limits to human survival have not been established for obvious reasons – it isn't exactly ethical to test how long people can survive without sleep, water, air, or food.

However, we can learn from people who HAVE survived incredible events and lived to talk about them.

Humans are capable of fascinating, incredible accomplishments.

Humans are capable of astounding feats, including some that seem to defy everything we know about the body. Consider the following documented athletic achievements:

• Sprinter Usain Bolt is currently the world's fastest human, with a top speed clocking in at 27.8 miles per hour.

• Freediver Herbert Nitsch descended 702 feet into the waters of Greece – a holder of 33 world records, he can hold his breath for more than 9 minutes.

• Aleix Segura Vendrell held his breath for 24 min 3.45 seconds, setting a world record (and beating the previous record, which he also set).

• Strongman Zydrunas Savickas has squatted and deadlifted 955 pounds and 903 pounds, respectively.

• Annette Fredskov, who has multiple sclerosis, ran 26 miles a day – every day – for a year. On the last day, she ran 52 miles.

• Rock climber Alex Honnold scaled the nearly 3,000-foot vertical rock formation known as El Capitan in Yosemite State Park without using ropes or other safety gear.

• Dean Karnazes ran 350 miles straight – which took 80 hours and 44 minutes – without stopping to sleep or eat.

• "Iceman" Wim Hof ran a half marathon above the Arctic Circle on his bare feet and stood in a container while covered with ice cubes for more than 112 minutes.

• At age 64, Diana Nyad swam 110 miles (between Cuba and Florida) in 52 hours, 54 minutes, 18.6 seconds.