To look, rather than to assume. A check is what turns a belief into a finding.
Old French eschec, from Persian shah (king), by way of the chess move announcing the king is under attack; the verifying sense grows from the game's language of testing and restraining, and the accounting sense (a written order for money) is a distinct branch of the same word.
To look rather than to assume — a check is what turns a belief into a finding that can be shown to someone else.