One of the deep dark secrets they don't teach you about this field is that you're going to spend a large chunk of your time preparing the data (sometimes as much as 75% of a project). I've had people ask me over the years why data preparation can absorb so much time and the answer really is simple:

Garbage in -> Garbage out

Data will drive your project to success or failure. It's imperative that we are diligent in exploring the data we have available and using the right portion of the data for learning.