Two selections from Human Action:

Both principles of cognition—causality and teleology—are, owing to the limitations of human reason, imperfect and do not convey ultimate knowledge. Causality leads to a regressus in infinitum which reason can never exhaust. Teleology is found wanting as soon as the question is raised of what moves the prime mover. Either method stops short at an ultimate given which cannot be analyzed and interpreted. Reasoning and scientific inquiry can never bring full ease of mind, apodictic certainty, and perfect cognition of all things. He who seeks this must apply to faith and try to quiet his conscience by embracing a creed or metaphysical doctrine.

Science does not give us absolute and final certainty. It only gives us assurance within the limits of our mental abilities and the prevailing state of scientific thought. A scientific system is but one station in an endlessly progressing search for knowledge. It is necessarily affected by the insufficiency inherent in every human effort.