The popular picture of rationality is certainty — a fixed body of proven facts that belief either matches or contradicts. But that is not how knowledge actually grows. Knowledge grows the way the philosopher Karl Popper described it: by conjecture and critique. We propose explanations, test them severely, and keep the ones that survive — always provisionally, always open to revision.
That process improves our understanding without ever finishing it. No explanation is ever proven beyond question; the best we can say is that it has been tested hard and has held up so far. Which raises a question the usual "faith versus reason" framing never asks: if certainty is never on the table, then how do we ever act at all?