This is essentially the relationship that Ohm's law represents.
I agree and the three simple formulas, I=E/R R=E/I and E=IxR is all one needs to know to understand the relationship. And until they really understand Ohm's law (and to 'think' in ohms law) they will continue to have trouble progressing in learning electronics. There is a reason almost all electronics fundmentals course start with DC electronics and Ohm's law and only then progress further.