Friends of Rachels includes, from left, Austin Yoshida, Tyreese White, Caleb Rodusky, Marco Garcia, Allison Padilla and Matthew Gunawan at a workshop on Sept. 2. (Leo Jarzomb / Staff Photographer)

Kindness should come as natural as breathing. Compassion should be a constant companion.

But sometimes the world beats people down. Sometimes they become so bitter and angry that they strike out, hurting others in the process.

Their rage can be dramatic. In April 1999, Eric Harris and Dylan Klebold opened fire at Columbine High School in Colorado, claiming the lives of a teacher as well as a dozen students. The two gunmen also injured 21 others, before committing suicide.

It was the worst attack on an American high school in history.