When a person believes in the tzaddik without any daat, it is possible for him to fall from that faith, because from faith alone it is possible to fall. However, if he has also daat—he comprehends intellectually as well—then it is impossible for him to fall.
כְּשֶׁהָאָדָם הוּא מַאֲמִין בְּהַצַּדִּיק בְּלִי שׁוּם דַּעַת, אֶפְשָׁר לוֹ לִפֹּל מֵהָאֱמוּנָה, כִּי מֵאֱמוּנָה לְבַד אֶפְשָׁר לִפֹּל; אֲבָל אִם יֵשׁ לוֹ גַּם דַּעַת, שֶׁמֵּבִין גַּם בְּהַדַּעַת, אֲזַי אִי אֶפְשָׁר לוֹ לִפֹּל:
When a person believes in the tzaddik without any daat, it is possible for him to fall from that faith, because from faith alone it is possible to fall. However, if he has also daat—he comprehends intellectually as well—then it is impossible for him to fall.