אַֽל־תִּ֭תְהַלֵּל בְּי֣וֹם מָחָ֑ר כִּ֤י לֹא־תֵ֝דַ֗ע מַה־יֵּ֥לֶד יֽוֹם׃
NO te jactes del día de mañana; Porque no sabes qué dará de sí el día.
Rashi on Proverbs
Do not boast Do not boast now concerning a thing that is destined to be tomorrow.
Rashi on Proverbs
for you do not know what the day will bear Perhaps the day will bear some evil that will nullify it.