WHY IS MACHINE LEARNING 'HARD'?

Summary from the TLDR Web Dev newsletter

Difficulty in machine learning (ML) is not primarily due to mathematics, but rather the need to build an intuition for selecting the right tools and debugging. Debugging in ML is exponentially harder than in standard software engineering due to multiple dimensions of potential issues involving algorithms, implementation, data, and model correctness. The long debugging cycles in ML, which can be days or even weeks, make parallel experimentation necessary.