ન આવડે લીખ તો વૈદું કરતાં શિખ, નકટીનું નાક કાપે તેવી છરી છે.

na āvaḍē līkha tō vaiduṁ karatāṁ śikha, nakaṭīnuṁ nāka kāpē tēvī charī chē.

Literally: If you do not know how to write, learn to practice medicine; it is a knife that cuts the nose of an already noseless woman.
What it means: Said of incompetent people who take up professions they are unqualified for, causing further harm.

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.