He turned his heart to worship other gos instead of being completely faithful to the Lord - 1 KIngs 11:4
Solomon was the proverbial riddle wrapped in an enigma
He was the wisest man who ever lived but he turned away from God and toward pagan idols
This turn led to the loss of everything he have accomplished - 1 KIngs 11:11-13
Despite God appearing to him twice and blessing him in every way, Solomon still turned to idols
Solomon's poor choices tained his service and led to big problems for the kingdom of Israel
It is far more important to perserve focus on the eternal prize God has for those who finish strong - 1 Corinthians 9:24-25