[Throw_Away_6389]

You can't know exactly what is best, but you can act to the best of your knowledge. Just because you can't do something perfectly doesn't mean you shouldn't do it as well as possible.

[AstralStorm]

The fun stuff happens when deontologist meets conflict between their moral or other laws...

It always happens and is a fact of life. That's how you can gauge how "lawful" someone is - using simple D&D model of morality.

The other axis is altruism vs egoism.

So lawful good is deontological altruist, while chaotic evil is non-deontological egoist. There are decent stereotypical descriptions in SRD.

https://open5e.com/characters/background.html