વરસા વરસા વ્યાસ કહે, વરસ્યા પછી જોશી કહે.

varasā varasā vyāsa kahē, varasyā pachī jōśī kahē.

Literally: The Vyas predicts rain, but the astrologer only speaks after it has rained.
What it means: Said of people who only make predictions or offer advice after the event has already occurred.

Also said as

ગુજરાતી કહેવતસંગ્રહ (Gujarati Kahevat Sangrah) (1923) · read from the scan by machine — the Gujarati itself is unchecked · English is machine-made and nobody has checked it yet

Heard it differently, or know we've got the sense wrong? Tell us — that is exactly the kind of correction this needs.