“If you can’t explain something simply, you don’t understand it well enough.”
This is patently not true, and its questionable if it can even be attributed to Einstein, but "when you have to choose between the truth and legend, print the legend."
Although it is not always true, I think it is a very useful maxim to try and stick to. You can gain a lot of clarity by boiling something down to a simple model, often having to look at a situation by its two extremes before seeing where in the middle you should be.
As the statistician George Box said, " there is no need to ask the question "Is the model true?". If "truth" is to be the "whole truth" the answer must be "No". The only question of interest is "Is the model illuminating and useful?"".