Equations. When we model things with equations, sometimes they don’t have a ‘solution’ at a particular place, unless we use the formal math rules of ‘imaginary’ numbers like i. Someone else in the comments mentioned electric conductance/resistance in circuits as an example.
I used to have problems with clumps. I still do, but I used to as well.
For the most part I now make things in batches. Hot chocolate, tea, whatever. With big batches I can use the mixing bowl and use the immersion blender. Nothing stays clumpy when you have a blade whizzing around at 3000+ rpm.