Learn deeply basically means being able to make amazing tools from the bottom to the top. Be an expert in the tool means being able to make amazing things with

Learn deeply basically means being able to make amazing tools from the bottom to the top. Be an expert in the tool means being able to make amazing things with it without necessarily being able to make the tool yourself. So low level versus high level. For example the majority of webdevs probably couldn't write V8 but they can make JS sing.