For any adventure like hiking I always take a top be it wool, fibre pile, fleece, or down, that is warm enough for the time of year to be enough for the night. I am also a fan of brew kits and carry one often; plus I carry a small firelighting kit that gets a fire fast with no faffing about.
So many times at the end of an adventure when the sun has gone down I stand there toasty and the rest of the group shiver because they didn't think far enough ahead. A long day expending energy and its taken a few hours more than expected are common. Too many people are too precise and plan too closely to what they think is enough. Too often its not enough.
Sometimes I am really popular when I break out my brew kit and have a hot chocolate steaming in my hand in minutes.
White ashen face is a give away... its even obvious on dark/black skin.
Loss of coordination with gibberish "I'm alright"... no you are not.
Once set in it takes a real effort and a good length of time to get that chill out. Its real damage and even after recuperation can set in very fast again if exposed to the same conditions a few days later.
Climatisation can help by being used to the climate, as those not used to it go down faster. But the pure cold physics of it make anyone susceptible.
Sweat after work next to the skin is a bad one and must be got rid of.
Lastly, there is a lot of lack of knowledge and know how out there especially as so many people are just tourists to an area. Locals generally know whats up.
I find fibre pile next to the skin one of the very best to get warmth into a deep chill. The rest is experience and being proactive. Good if you recognise it before it becomes a real problem, but once set in then its a priority and requires action fast. Easier with help, difficult if alone.