Machine learning Tools vs theory

Hello,

I am starting to find machine learning interesting but the discussions I have had with some people always leaves me with a question. All these guys know how to use tools but they dont really understand what happens behind the scenes.

Isnt it important to understand why something in machine learning works and what are the difference before using the tools that give outputs based on stackoverflow discussions?

Or the only way to understand machine learning is to use tools and learn progressively?

I would love to know what you guys think, I will be working on project soon which might involve machine learning and I dont want to take it up without understand what machine learning involves.