Throughout the history of ideas there have been sprouts of thought that claim the mind to have a naturally transcendent capacity, dwarfing the commonality of our other faculties, never leading us astray.
This is not so, though its persuasion is terribly subtle. Thinking can be easy and regular such that we often drift from one project to the next, presuming we'll gather all the data and start down the right path every time.
We think a lot, but we don't always think rightly. The effects of sin taint our ability to reason as much as our ability to choose — yes, we are that broken.
John Webster writes,
Like all other aspects of human life, reason is a field of God's sanctifying work. Reason, too — along with conscience, the will and the affections — must be reconciled to the holy God if it is to do its work well (Holiness, [Grand Rapids: Eerdmans, 2003], 10).
We're going to think today and unless we remember that our thinking is fallen we're going to operate in some mode that functions as if it doesn't really need the blood and victory of Jesus, naively entrenching ourselves in the mire of self-sufficiency.
So let us pause for a moment — stop and think — and let us be overwhelmed that our thinking has never produced one good thing in and of ourselves. . . . (see, even that thought about our thinking is not from us). "What have we thought right that we have not received? If then we received it, how can we boast as if we did not receive it and go on thinking like we're not desperate for grace?"
For more on this subject, see Chapter 5, "Rational Gospel, Spiritual Light" in Think: The Life of the Mind and the Love of God, (Wheaton: Crossway, 2010), 69-80.