I've been trying to get back to at least as much control theory as I understood in my college days, and this is a pretty neat explainer of the notion of stable vs. unstable control systems (what they intuitively mean, without diving headlong into the math of how we get the systems model to tell us if we're looking at a stable / unstable one).

https://jbconsulting.substack.com/p/you-need-to-know-what-right-half