A countdown clock that continued to increase past 00:00; a security guard whose face turned ghostly-white in an instant; a lack of response from the Columbia crew to repeated calls from Capcom/Astronaut Charlie Hobaugh; and the words of "Get ready," uttered quietly from the lips of Steve Lindsey, told me that it was time - time to be strong in the face of true adversity.

It was the most difficult day of my life; even harder than when my father died, as that was what we were expecting. I do my best to describe the day's events in my book, but suffice it to say I felt a huge emptiness inside and it is a burden I still carry today. That day changed me inside; it made me much more emotional than I can ever remember being. It tested my faith and it still tests me.

But it never dulled my dream to fly in space. It only strengthened my resolve. We (NASA) would figure this out. We would make it safer than before. That's what we do. That's "how we roll."

Spaceflight is dangerous. Spaceflight is hard. We must keep that in mind as we move forward into the era of commercial spaceflight endeavors, lest we forget the lessons of our past.

Godspeed Challenger; Godspeed Columbia.

This from Clayton Anderson's answer to What was it like to watch either the Challenger or Columbia space shuttle disasters live? on Quora.

Today, of course, is the twelfth anniversary of the Columbia disaster, and earlier this week marked the twenty-ninth of Challenger.