I prefer the labels "predictable" vs "unpredictable" work. For example, I've been experience the difference between research and back-end web dev work lately, a

I prefer the labels "predictable" vs "unpredictable" work. For example, I've been experience the difference between research and back-end web dev work lately, and the main difference is that for research you don't know if it will pan out, while for back-end work you're almost always making incremental progress towards the end-goal. But I wouldn't necessarily call research "harder", it's just different. It's usually more difficult conceptually, but there's also way less stuff you need to keep in your head at the same time.