Hezekiah realized that he had no resources or "no strength" left to fight the Assyrians. Sennacherib king of Assyria had already attacked all the fortified cities of Judah and captured them (36:1) and now he was coming for Jerusalem. Unless God intervened they were ruined.
Oswalt in Constable's Commentary, writes: "This kind of admission of helplessness is frequently a necessity before divine help can be received. So long as we believe that we only need some assistance, we are still treating ourselves as lord of the situation and that latent pride cuts us off from all God would give us."
So often when we are facing a difficult situation we ask God for some assistance rather than admitting how powerless we really are. Our independence and self-sufficiency (or our "latent pride") gives us a false sense of confidence and persuades us that we can manage with just a little help.
We see ourselves as "lord of the situation." We tell ourselves others have faced worst situations and survived so surely we should be able to handle whatever comes. This attitude stops us from asking God for all the help we need.
On both occasions when Hezekiah received bad news (v1 & 14) his first reaction was to go to the temple of the Lord. He prays for the people (v.4) and God's reputation (v.20). By his actions Hezekiah acknowledges his inadequacy to resolve the situation.
It requires faith to respond like this, to say to God unless you intervene we are doomed but humility is the pathway to the resources of God.