Why we can't always stop what we've started. When we try to stop a body movement at the last second, perhaps to keep ourselves from stepping on what we just realized was ice, we can't always do it -- and neuroscientists have figured out why. Source 4r.
Some times this has to do with the laws of Physics where a mass in motion can sometimes be hard to stop suddenly. At times it can be but many times it just fails to stop on a dime.