There are 14000 "known" nuclear war heads on planet earth.
The people who have the ability to deploy them are arguably no more intelligent or rational than you or I.. in fact, I would argue that they are likely less rational.
Based on human history, they will get used eventually. They were made. They're likely to be used.
Nobody eve thinks the worst will happen, until it does.
I currently think it's a low probability.. but there is a possible series events that would lead to nuclear war. Unlikely, but it exists.
We are closer to nuclear war today than we were 2 weeks ago.
We are without a doubt entering a severe global recession. Possibly a depression.
A global depression could very quickly alter global human psychology. Alter it in a manner that makes large scale global war more socially acceptable.
Fear, anger, and desperation are some powerful emotions. Especially when it's on a global scale.