Someone made a comment that breaking halakha = sin. And while I can think of very many halakhot that I agree with this idea that breaking the halakha is de facto a sin. But there are other halakhot, halakhot that many of us don't even keep anymore. Halakhot about which shoe to put on first. Halakhot that only appear in the last few hundred years by all accounts and we're not followed before, did all prior Jews sin for not having followed it before it became common practice?

So is breaking any halakha regardless of content, practice or age/history always a sin? If so, why. If not, why not?