Engineers work in a world of exactness where the laws of physics and mathematics operate in seamless precision. Things are either right or wrong; they either work or they don’t. Mistakes shouldn’t happen–and yet they do, far more than they should. Failures occur because human beings get in the way and add a variable the science didn’t anticipate. But while the laws of nature are unchanging, humans can learn from our past mistakes to avoid future disasters.

1986 Challenger Explosion:

The space shuttle Challenger exploded 73 seconds after launch because of a problem NASA engineers already knew about. In fact, as the investigation discovered, NASA personnel had realized that the “O-rings,” which failed on the Challenger, had a problem in cold weather nearly a decade earlier. For this reason, the Rogers Commission called the explosion an “accident rooted in history.” The report further concluded that there was “a conflict between engineering data and management judgments, and a NASA management structure that permitted internal flight safety problems to bypass key Shuttle managers.” The painful lesson is clear: human-related concerns, such as budgets and flight schedules, cannot trump science.

2000 London Millennium Bridge:

Although there was no loss of life, the opening of London’s Millennium Bridge still stands as one of the more glaring engineering failures in recent memory. When the beautiful bridge opened on June 10, 2000, nearly 100,000 crossing pedestrians noticed that the traverse wobbled horribly. Authorities closed the bridge two days later while engineers scrambled to find out what went wrong. They learned that the bridge designers had failed to account for the effect of pedestrians matching their footsteps to the slight sway of the suspension bridge–an effect exacerbated by the bridge’s sleek design. It wasn’t an unknown problem; indeed, soldiers marching over a bridge are often instructed to break cadence to limit the effect. Yet somehow this basic point of bridge building got lost during the design of Millennium Bridge. When the bridge opened, it was hailed an as engineering and artistic masterpiece. But its lesson is that beauty can never take precedence over form and function.

2010 Deepwater Horizon Explosion:

A multitude of mistakes and failures contributed to the worst environmental disaster in U.S. history, in which 11 people died. But according to the New York Times, one of the more glaring was that rig workers feared retribution if they voiced their safety concerns. In the weeks and months leading up to the explosion on April 20, 2010, workers noticed numerous safety and structural problems, but these concerns were either unvoiced or ignored. The lesson seems to be that a culture that punishes whistleblowers, particularly in an engineering enterprise, is one that is asking for failure.