To be honest I think most of us experience brief moments of personal cognitive dissonance in every day life at one time or another whether or not we have been in a cult.
In childhood, it's a daily occurrence often encoraged by parents, eg, small children believe in Father Christmas, magic powers, guardian angels and fairy tales even though logic is clearly against it.
Even when parents insist something is not true, and the child understands logically it's not feasible, the emotion can remain very real and be more powerful than the facts, eg, monsters under the bed, wolves in the forest who could swallow your grandma whole, or an invisible spirit who will punish you if you are badly behaved.
My own childhood cognitive dissonance was not harmful overall..... contrary to all logic, I wanted to believe my teddy bears and dolls came alive and had a party when I was sleeping; and when I fell over, I wanted to believe my Mum's kiss really was magic and miraculously took away the pain of a scraped knee.
As an adult, I am by nature sceptical and try to be rational in all circumstances, but I sometimes catch myself even now.
Take the case of a family member whom you love and always assumed was kind and good and shared your own high principles and moral code. Then you catch them deliberately lying and cheating or being cruel. Cognitive dissonance can click in as you really don't want to believe your relative is flawed, and it allows you to make excuses for them and continue to feel and act as if they are innocent.
It's sadly too easy to use CD to hide facts and evidence from your conscious mind, especially when you have a lot of past history tied up with your belief and especially hard when admitting you were wrong will badly dent your pride and self esteem.
Thats why I deeply admire all you ex JWs who have destroyed the power of cognitive dissonance in your lives and had the humility to face the fact you were wrong, and admit it to others. Not easy but shows a great strength of character.