What the hell is cybernetics and why should I care?
The word cybernetics comes from the same root as the Greek word for steering, specifically the art of steering.
Now when you steer it's because you want to go somewhere and as you set out to get there you're blown off, of course you can't go straight, you have some backs and fourths.
Cybernetics involves the idea of using feedback loops from your actions comparing to your defined goal so you can correct your trajectory.
The word feedback has been introduced in our language in the middle of the 20th century by a bunch of extremely smart people who said, hey there's this thing that systems do which is have a goal and try to get to the goal and they use information to do that so let's call that feedback.
The reason why we should care is because intelligent or autonomous systems such as human beings that interact with their environment also have a goal and they use feedback to get to their goals so cybernetics as a science of feedback, information, and goals is incredibly valuable in many different disciplines.
Systems have limited capacities, if a boat is sailing using wind, the boat is limited by the speed and the direction of the wind. The boat have a range of capacity to continue it's trajectory despite the wind condition. Variety is the capacity of a system to run with environmental constraints.
For example, a body have a requisite variety to keep the body temperature in check despite the outside temperatures within certain limits.
Being aware of the requisite variety of ourselves and our conditions/environment is absolutely phenomenally important to achieve a goal.