It is not smartness. Anybody can be careful and smart. A man walking on a wire three hundred feet above ground is careful. Remember those gymnasts performing all kinds of balancing feats. Numerous daredevils who climb very steep mountains, across rocks, slippery places, rivers, and so on are very careful.
Many thieves are very smart and outwit the police.
Many drug dealers, bank robbers, criminals are very smart. None of them can be considered to be mindful. Mindfulness is that state of mind which reflects upon itself not to get caught in greed, hatred and ignorance, which cause suffering to yourself, to others or to both. This is the miracle of mindfulness. When you practice mindfulness you can learn to do most difficult things easily.