1. Even though Alexander knew about Darius's skilled army, Alexander fought the Persians showing again, him being strong-willed.  
2. Because of the Persian Navy (best in the world) letting Alexander pass them by instead of fighting, it might have cost them the "easy win."
3. The Persians asked for peace, but Alexander didn't give in resulting in Alexander and his troops slaughtering the them and winning.
       There was a big goal that Alexander wanted to accomplish and that was to overpower the Persian empire. The Persian empire was a huge force. It was said that they would have a million men prepared in case of an attack. The king of this powerful army that had no one to fear was a man named Darius III and called "The Great King." Even with these intimidations, Alexander sailed to Asia. While Alexander came near to Persia, the Persian Navy, saw Alexander's army, but having total confidence in their army they let him pass them by. On shore, the first thing that Alexander did was visiting Troy because that was the subject of the Iliad which Alexander loved. Some time after this, he marched down into Persia with 35,000 men. Darius arrogantly sent a small unit, probably even smaller than Alexander's and Persian cavalry to go down to the Granicus River to fight Alexander and his troops, while he would not go, thinking that this would be an easy win. The Persians lined up in their usual formation which made it very difficult for Alexander because they had to cross a low and fast river with high banks. Alexander lead his troops when they attacked. His men had a hard time getting up the slope at first, but they had managed to do it. Alexander went after Mithradates (son-in-law of Darius), but just as Alexander was driving his sword into him, another Persian cut Alexander in the head with his sword. With blood gushing out from his head he fell unconscious. After awhile Alexander's consciousness had come back, and he was able to get back up on Bucephalus. Alexander assembled his troops and struck further into the Persians. The Persians asked for peace, but Alexander didn't give in. He and his troops killed the Persians left to right and then, after thousands being slaughtered, Alexander won.