What's the toughest feature you've built that needed a lot of trial and error?

I'd say animations are some of the trickiest features I've worked with. Especially custom 3D animations, they can be such a pain to replicate according to client requirements!

I tackled real-time collaborative editing, which involved conflict resolution. It took about three weeks to get most of it working, but I'm still haunted by the edge cases, especially simultaneous deletes in overlapping ranges!

Not a developer, but I created a custom inventory tracking system for my book sales across various platforms. Synchronizing everything to avoid double-selling copies was a total nightmare. I learned a lot through trial and error!

Building a multi-tenant permission system was a challenge for me. The resource could be shared across different organizations, but managing varying permission levels for each member was complex. I read some academic papers on access control models and tested several approaches before finding the right one. The simpler methods just didn’t work, and figuring that out took a lot of trial and error.

One of the toughest challenges I've faced was connecting with legacy systems that came with incomplete documentation. It was a real headache trying to figure everything out without clear guidelines.