Diligence is the remedy the scheme sets against acedia, and understanding the pairing requires taking acedia seriously as something other than laziness. In its monastic origin, in Evagrius and then in Cassian, acedia is the noonday demon: a specific and dangerous condition in which the cell becomes unbearable, the work loses its point, and the monk becomes convinced that the life he chose was a mistake. It is closer to what would now be described as a collapse of meaning than to idleness, and it was regarded as the most serious of the eight thoughts precisely because it attacks the will to continue at all.
The contrary virtue therefore cannot simply be industry. The manuals give diligentia, industria and sollicitudo, and what they mean by them is a wakeful attention that keeps returning to the work whether or not it currently seems worth doing. Cassian's prescription is famously unspiritual: stay in the cell, do the manual labour, do not go visiting. The virtue is built out of persistence rather than enthusiasm.
Something was lost when the list moved out of the monastery. As sloth came to mean idleness in ordinary preaching, diligence came to mean busyness, and the pairing turned into an argument for hard work that neither Evagrius nor Cassian had made.
Diligence has no fixed attribute in art, and the atlas draws none for her.