It often happens that first and hastily spoken words have to be regretted sooner or later.
It is not that there is no opportunity to correct what has been said already. But those words may have already been analysed and etched somewhere at the back of the listener's head. Usually, what you say first is what you mean the most. But there are occasions where you'd want to change your words. Then why not be careful and make it a point to always think before speaking however sure you are? Haste indeed makes waste... haste harms, haste hurts.