I disagree with the other responses. I think it's both. You can get very quick results and feedback for experiments related to implementation. Code compiles or doesn't, tests pass or they fail. But whether you actually built the correct thing is definitely "wicked." A lot of times subtle bugs and user feedback surface weeks or months after the fact. It can be very hard to find out whether what you did worked for the business need, which is ultimately the main point of the job.