I think overcoming UX issues while still holding on to some of the trustless / self sovereign nature that Bitcoin is ideally about. There's trade offs to everything, and looking at how each Lightning wallet solves certain aspects to provide a decent UX is interesting. Some are very trusted, some are very unknown publicly, etc.

But that's also what makes Lightning such an interesting place to work in. We all get to experiment with different models and see what works and we all gain that knowledge and can improve.

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