C. F. Keil and Franz Delitzsch on Proverbs 28:18

Pro 28:18 18 He who walketh blamelessly is helped,      And he who is perverse in a double way suddenly perisheth.

The lxx translate תמים by δικαίως (as the accusative of manner), Aquila and Theodotion by τέλειος; but it may also be translated τέλειον or τελειότητα, as the object accus. of Pro 2:7. Instead of עקּשׁ דּרכים, Pro 28:6, there is here נעקּשׁ דּרכים, obliquely directed in a double way, or reflex bending himself. At Pro 28:6 we have interpreted the dual דּרכים rightly, thus בּאחת cannot refer back to one of these two ways; besides, דּרך as fem. is an anomaly, if not a solecism. בּאחת signifies, like the Aram. כּחרא, either all at once (for which the Mish. כּאחת, Aram. כּחרא), or once (= בּפּעם אחת), and it signifies in the passage before us, not: once, aliquando, as Nolde, with Flacius, explains, but: all at once, i.e., as Geier explains: penitus, sic ut pluribus casibus porro non sit opus. Schultens compares:

“Procubuit moriens et humum semel ore momordit.”Aeneid, xi. 418.

Rightly Fleischer: repente totus concidet.