אל תתהלל ביום מחר כי לא תדע מה ילד יום
Do not boast about tomorrow, for you do not know what the day will bear.
Risk is theoretically measurable, uncertainty is not. In modern Hebrew, these are אי ודאות, אי בטחון, respectively.
Do not boast about tomorrow, for you do not know what the day will bear.