Considering the historic stock market events, how has the function of the "circuit breakers" evolved? They were initially used to curb the fallout of the 2008 financial crisis, but didn't activate during the Black Monday 1987 crash. They were used to prevent the 2008 financial crisis but failed to halt trading during the COVID-19 market crash. They were first introduced after the Black Monday 1987 crash to pause trading after a 7% decline, but couldn't prevent the 2008 financial crisis. They were triggered again in March 2020 during the COVID-19 market crash.