Back when I started, you could fix most things with a wrench and a keen ear....

https://dlf-ne.org/beyond-the-code-what-an-advanced-diagnostic-platform-actually-does-for-your-shop/

Back when I started, you could fix most things with a wrench and a keen ear. Today, your car is essentially a network of computers. Basic OBD readers only scratch the surface by reading a few generic codes