Music and music theory the holistic way. Understand one concept, understand all

I have been teaching music for more than half a century from complete beginners to advanced musicians. As a kid, I found music to be a struggle until someone started teaching me in a holistic way. If you can understand one small aspect of music, then there is no reason why you can't understand all aspects of music since everything is interconnected.
For example; once you understand why G major / E minor has one sharp then you can understand why C# major / A# minor has seven.