Job wrestled with why God allowed his suffering. His confession acknowledges that God's 'thoughts' or purposes might be beyond him, yet still perfectly controlled by God.
The phrase translated as 'no purpose of yours can be thwarted' points to the unhindered nature of God's plans. While Job struggled to grasp why God allowed his suffering, he ultimately recognized that God's wisdom and power meant His purposes, though mysterious, were always in motion and always effective. This isn't an excuse for evil, but an affirmation that God, in His infinite wisdom, orchestrates all things, including what may seem like setbacks, towards His ultimate, good, and sovereign ends.