[jessewmc]

I mean it could be both. I could imagine that people can become conditioned to it in such a way that they are functional in cold water if they do it on a regular basis and/or were brought up with it.

But I've jumped in glacial lakes before (not on the regular) and it would become life threatening for me very quickly. It's quite scary.

[watwut]

Yes, you condition yourself to it. You become more resistant over time and can stay longer and longer.