Hezekiah did not learn what God wanted him to learn. He was one of Judah's good kings, but still struggled to let God change his heart. After his recovery from a deadly illness (a situation in which God intervened with divine healing), he proudly received a diplomatic envoy from Babylon and gave them the full tour of the treasures of Jerusalem. Hezekiah is proud and foolish.
God wanted the king to think towards the future of the nation. But Hezekiah had a tendency to be short-sighted. When he fell ill, God's message through Isaiah was for the king to "set his house in order" (Isaiah 38:1). This was a call to reorder priorities. It involved preparing his sons to lead well and entrusting the kingdom to their stewardship. But Hezekiah's thoughts in this incident show he paid no attention to the warning God gave him. He was content for the nation to thrive only in his lifetime. He gave no thought to the future, but was content to live "in the moment". He sold his future at a bargain price at the first opportunity that came his way.
Ironically, the Babylonians to whom Hezekiah had just issued the "back stage pass all access tour tickets" would one day return in the very near future to burn Jerusalem to its foundations. The would plunder the treasures of the city and take the people captive away from it. The king's sons would be castrated and led away as eunuchs to serve the Babylonian king. Hezekiah's line would end because of his nearsighted contentment with the politically expedient NOW. Selfishness will make us short-sighted. And a good future found in obeying God can be lost by present satisfaction with a mediocre status quo. It is a stupid mistake to make.