What is the most difficult part of programming?

I am building a startup around the developer productivity space.

If you are okay with a 15 minute Google meet chat, please help me out!

The gist of the question I want to ask via Google Meet is “what is the most technically difficult or time consuming part in your day to day programming”

If you leave any comments, I can DM!

p.s notice it is “technically difficult or time-consuming” so it excludes meetings, culture, any nontechnical stuff