I recently went to a concert of Australian guitar player Tommy Emmanuel. Since he stepped on the stage everyone in the crowd seemed to be perplexed how only does he manage to play so well. Tommy can play pieces which are so difficult that other bands have two guitarist to play the same. How is he doing that?
At the age of 10 Tommy had a band with his older brother. His artful brother let young Tommy to play all the sounds in the background so that he can excel as lead guitarist. They listened to the radio songs and learned the music by listening. One song was particularly difficult and when Tommy finally managed to perform it he run off to show to his mom. From her he learned that the song is actually played by two guitarist. If he would have known maybe he would never tried to play two guitar lines together.
Similar situation happened to young student George Dantzig. One day he came late to the lecture and quickly he copied what he believed was a homework into his notebook. Only after he handed the solution he found out that it was not a homework but so far unsolved statistical equation. Dantzig however did not think about it as of impossible mathematical task but rather as a difficult homework and he managed to find a solution.
We can see many examples of achievements caused by simple ignorance of impossibility of the task at hand. I myself believed that work with google maps is difficult. After playing with them for about 2 hours I discovered that it's actually quite simple and even I can use google map api pretty well.
In conclusion: Some deeds are impossible until there is a dolt who doesn't know it and succeeds.
If you know it's possible
Opposing barrier occurs when you are limited by missing knowledge that it is possible. If all your friends would be organizing sport events you would probably be able to prepare a race or two. Though if your whole life is filled with something else let's say art you would probably never get to held a sport competition even though you might have great idea and business opportunity in your mind. You would fail because you would never try - thinking that it is too difficult.
In a moment we realize that something is achievable we're half the way to succeed.