None of us are reaching our full mental potential at all times, and that's completely okay and normal. Our brains do so much daily work that we'll never fully recognize, and everyone processes differently and carries a different load. Which is to say, having a few brain farts isn't anything to beat yourself up for.
However, we've all met that person who never ceases to amaze us with how disconnected from the world, and how much confidence they pour into the least informed opinions. Some people have the personalities of a drunk and sleep-deprived proclamation in human form, and it's baffling to behold.
A customer who thought he should be able to get the Jordan Bred 11s for 90% off because of two "coupons" he had. One of these coupons was a print out of a 70% off clearance promotion from Nike's website and the other was a 20% off coupon from Payless that expired in 2017. I've never been more confused, frustrated, and exasperated than I was during the 10 minute interaction where myself, two managers and a customer tried to explain to this man why this wasn't going to happen.