What is the distinction between knowing and being certain?
The world is flat. The earth is the center of the universe. Pluto is a planet. The fifth postulate. Milli Vanilli is awesome. Remember when these statements were inarguable and certain?
Being certain is a state of mind which stops the individual from exploring, seeking new information and further knowledge. Knowing something--even includes knowing that what you know today--may change tomorrow by gathering of new data, Therefor knowing is open to development but not being certain.
Certainty implies that what you know is undeniably true. Feeling certain about something is a mental thing rather than evidence of fact. Feelings like certainty come from primitive areas of the brain and are independent of active, conscious reflection, and reasoning.
So, is it logical to use logic all the time?
No. If you do so in every aspects of life it will turn you crazy. Why? Because logic is just one way to explain things; like mathematics which it is a way and a language to show the measures and rational issues and so on and if you want to use logic to get the best decision (which I had done so far) you will get to this point: TAKE IT EASY! LIFE DOESN'T NEEDS THIS MUCH OF ATTENTION.
However, it is illogical to think that most people were capable of using logic all they time. They are not. Even a logical extremist such as myself has trouble maintaining my logical decorum at times. But that doesn't mean it’s not worth the effort.
Logic as an abstract concept should be right all the time. But, the human mind can break this perfection with its imperfect nature (ego, emotions, etc), the emotional drive comes from self-interest and survival instinct. Computers are the most logical things ever. It go wrong, however, if you feed it the wrong data.
Logic is a function of cognition. Cognition is a function of consciousness and self-interest. Without self-interest, logic would not exist. Reality doesn't need to be "understood" or to make sense. In fact, without consciousness, reality would have no significance whatsoever. Neither reason nor logic is external to cognition. Logically speaking, logic existing outside of cognition is illogical. You are free to show me otherwise.