Orberg in LLPSI Cap XXVI scribit: ‘..sed omne consilium fugiendi me delectat, ac tu id quod semel excogitavisti perficere soles’.
Nonne illa sententia eadem est ut haec: ‘atque quod tu semel excogitavisti id soles perficere’
Nonne ‘id’ = ‘quod’ ? - i.e. both refer to the same thing
‘…THAT which you once solve usually complete IT.’ or in modern parlance: