“Sitting and waiting for something to happen was the worst kind of torture.”

Source: To Sir Phillip, With Love

Source: I'd Tell You I Love You, But Then I'd Have to Kill You

By The River Piedra I Sat Down and Wept (1994)
Variant: Waiting Hurts. Forgetting Hurts. But not knowing which decision to take is the worst of suffering.
Source: By the River Piedra I Sat Down and Wept

Jace to Imogen, pg. 303
The Mortal Instruments, City of Ashes (2008)

Scholastic interview (1998)
Context: When you're getting ready to launch into space, you're sitting on a big explosion waiting to happen. By sally ride. So most astronauts getting ready to lift off are excited and very anxious and worried about that explosion — because if something goes wrong in the first seconds of launch, there's not very much you can do.

Source: Absolutely Normal Chaos

About the origin of his interest in biology in an "Interview with George Gamow", by Charles Weiner at Professor Gamow's home in Boulder, Colorado (25 April 1968)

Source: Life, the Truth, and Being Free (2010), p. 26

As quoted in Jet magazine, Vol. 67, No. 2 (4 February 1985), p. 40