“As long as she thinks of a man, nobody objects to a woman thinking.” ― Virginia Woolf

And to an extent it is true. People form opinions, it is natural and not a good thing. Whether a person wants to or not, the second they learn a new fact they make an opinion on it. There is one exception  fora person making an opinion. If they don't think about it at all. 
I often try to block out thoughts that are not pleasant, thinking of something depressing and sad. Thinking of possible starving children in Africa, not the same as thinking of unicorns and homework. I couldn't have a stereotype for Africa because before reading Things Fall Apart I had not even thought about it. Realising that I had been so blind to the rest of the world though did make me thing of things that have been going on with a new clarity, accepting the bad and the good of the world.