This quote indicates that things can frequently seem too tough or difficult to achieve till someone actually attains them. Nelson Mandela is recommending that we ought to not give up on our goals even if they appear difficult initially. With effort and determination, we can achieve even the most complicated tasks.
"What is real is not the external form, but the essence of things... it is impossible for anyone to express anything essentially real by imitating its exterior surface"
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair"
