Why alexander the great didnt conquer the whole world?

                     Why alexander the great didnt conquer the whole world?
Everone knows  Alexander the great had an ambition of conquering the whole world. But he didnt succeed. Here is the story explaining the reason.
Long ago, there was a kingdom in Greece. Its king suddenly died due to some reason. He didnt have any children also. All the  people were worried as whom to crown king? At that time, a voice heard from the sky saying " whoever comes first to their kingdom in tomorrow morning, he should be crowned king." People waited for that person.
Next day morning , a businessman leading his cart to the kingdom for his business , was seen by people. They approached him and crowned him king. He was overwhelmed. He was a good administrator. Once he tied his cart to a nearby post and tied a magical knot to it. He said "whoever will untie the knot and free the cart, he will conquer the whole world". Hearing this, many people came to try their luck. But no one succeded. The news spread.
It was heard by Alexander, the great. Even he had an ambition of winning the whole world. He decided to go to the venue. He went to the place. Alexander tried to untie the knot. But he didnt succeeded. Getting insulted and glowing red with rage, Alexander took his sword and cut the rope tied to cart itself. Now the cart is free. But knot is still there.
Alexander didnt untie the knot as the condition said. Instead he cut the rope itself taking the easy way. In the same way, eventhough he conquered many places, he could not conquer the whole world. He died while returning to his place. Thus, the condition put by king as regarding untieing the knot was true.