We impute reality to that which we perceive, and then proceed to act on the basis of that mere imputation. If at some point we encounter indisputable evidence of our mistake, we are often surprised, even genuinely shocked. We are relieved that this is a rare occurrence.
Consider, however, the possibility that we are always imputing reality to our perceptions, and rarely see through our mistakes.
You want proof? Look around you at the countless people that are making evident mistakes. While their mistakes may be evident to you, they are apparently not so to their perpetrators.
Is it possible that our perceptions deceive us on a regular basis, that imputing reality to what we perceive is an ongoing process? Is it possible that things are not as they appear? Is it possible that our cherished certainties cannot withstand analysis?