What is Difficult?

"We often say: "Thinking is difficult."

What does this really mean? Why is it difficult? - It is almost like saying "Looking is difficult". Because looking intently is difficult. And it is possible to look intently without seeing anything, or to keep thinking you see something without being able to see clearly. Looking can tire you even when you don't see anything." (Wittgenstein - Culture & Value, 1948)