Although people speak and act so impulsively that they are not aware that a thought has gone ahead, that doesn't mean there was none. It just means that mindfulness and clear comprehension were lacking. Our mind is the most precious asset we have. No jewel can compare with it, because the mind contains the seed of enlightenment. Unless we use it properly, we're foolishly burying a jewel in the dirt.
People often do so, primarily because they have had no training otherwise.
When we recognize that we have this most precious jewel of a mind, we will guard it from being scratched, bumped and dirtied, losing its luster and brilliance, but rather make sure that it remains pure and luminous and thereby make good kamma. The action itself, the Buddha said, is not of the foremost importance, it's the intention behind it. Even generosity can be extended from a wrong motivation. If the intention is to store up some merit for the future, that's rather selfish. If it's done out of compassion for those who have less, that is the ideal way.