大乘百法明門論開宗義決 1.198

1.198

憍唯癡俱與慢解別者。謂癡通與諸惑相應故與慢俱。憍緣自性染著醉傲。慢緣地起高舉陵人。行解既殊不得俱起。

"Arrogance accompanies only delusion, and its understanding differs from conceit": that is, delusion generally associates with the various afflictions and therefore accompanies conceit. Arrogance takes one's own nature as its object, being defiledly attached, intoxicated, and proud; conceit arises based on status, elevating oneself and looking down on others. Since their mental grasps are different, they cannot arise together.