Why is machine learning hard?

Its not just the maths, algorithms, domain intricacies involved in any machine learning implementations that are hard challenges. The hardest problem is how to debug the whole kaboodle.

… machine learning is a fundamentally hard debugging problem. Debugging for machine learning happens in two cases: 1) your algorithm doesn’t work or 2) your algorithm doesn’t work well enough. What is unique about machine learning is that it is ‘exponentially’ harder to figure out what is wrong when things don’t work as expected. Compounding this debugging difficulty, there is often a delay in debugging cycles between implementing a fix or upgrade and seeing the result. Very rarely does an algorithm work the first time and so this ends up being where the majority of time is spent in building algorithms.
Why is machine learning hard?

This is spot on.