The prophet Daniel lived an incredible life that was marked with success and favor at every turn, and the Bible explains what made this possible.
From Jon Courson's commentary on this passage:
"Darius realized there was an "excellent spirit" within Daniel. What was this excellent spirit? The Holy Spirit. Daniel interpreted dreams. He prayed with effectiveness. He understood visions. He moved in prophecy. He experienced the miraculous. In other words, he was a man who was filled with the Spirit. That's what made him so successful all the days of his life. In 2 Chronicles 16:9, we read that the eyes of the Lord go to and fro throughout the whole earth, looking for a man in whom He might show Himself strong, whose heart is perfect toward Him. Our Father is still looking for men and women in whom He can show Himself strong - as He did with Daniel."
I love the NASB version of this passage, it says Daniel "possessed an extraordinary spirit". In addition to the Holy Spirit, I believe this also means that Daniel lived a life of excellence. He was the epitome of an overachiever. Daniel 1:20 says this about Daniel and his friends,
Remember that Colossians 2:3 states this about Christ,
The wisdom and excellence that Daniel possessed came straight from the source of all wisdom and knowledge, our Lord.