I'm a big fan of Mike Duncan's history of Rome podcast and have read a few other books on the Romans (secondary sources but of reasonable academic quality: now reading Polybius).

One theme that keeps coming up, especially for the Republic and early Empire, is the idea that the Romans had an unusual capacity to keep going after massive defeats: to not know if they were beaten. Including e.g. in the Samnite Wars, various points in the Punic Wars but especially after Cannae. Linked to this seems to be the idea (not always but often followed) that the only acceptable end to a war is the enemy 'losing' (preferably unconditional surrender, but at the very least until the late Empire they seem to have only really considered peace treaties after a major victory, not really in the aftermath of defeat, and the idea of 'Terminus' and that it's sacrilege to reduce Rome's boundaries (have only come across this last in Mike Duncan's podcast).

This makes a lot of sense to me as something that could make a real difference given the uncertainty and fortunes of war: if you just refuse to surrender when you seem to be clearly doomed, there's always a chance something will come up!

Linked quote from Polybius (book 1 section 37 Waterford translation) which identifies both positive and negative aspects: "Generally speaking the Romans rely on force for everything. They feel obliged to finish anything they start and regard nothing as impossible once they have made up their minds. This forward impetus often brings them success, but sometimes they conspicuously fail, and it is most likely to be at sea "

It's not clear to me if this was really a distinctive thing or is more part of Rome's self-mythology. If it is real, do we know why? Obviously traditionally people would have just said something about national character, but can we identify reasons for difference between Rome and others in terms of e.g.

- Resources: Rome seems to just keep raising more legions after being slaughtered in a way that others don't and I'm not sure if this means that the other combatants can't for economic/manpower reasons

- Citizen army and citizen identification with military success: e.g. Carthage relying on allies and mercenaries might mean that it runs out of money whereas Rome is drawing more on its own citizenry so their desire to win and thus willingness to fight matters more: in this sense Rome might have managed to act as a state how often factions only manage during intense revolution or civil war: notably Polybius mentions (Book 1 Section 72) in Carthage's mercenary war that when Carthage's allies rebelled the women of the city sold jewellery to contribute to the warchest etc whereas (Section 59) in the case of Rome the leading citizens funded ship-building for Rome itself with a mix of patriotism and the hope of reward in victory

- Political institutions and the incentives they create on the leadership: (this might suggest it was formed with Republican institutions and then persisted into the Empire through self-identity). E.g. did the one-year limit of the Consuls mean that nobody would surrender in* thei*r year? Notable that the Fabian strategy which somewhat conflicts with the 'brute force' approach required a dictator and even then was stopped by a population who wanted Rome to gloriously fight and win

- Military institutions: did the regular structure of legions etc. mean it was easier to just raise more men and fit them into the cookie-cutter whereas in Carthage armies were diverse and you needed to work out ways to combine the various troop types

- Other things???