OK... I doubt this means the cynefin framework type of Complex. That's what I use though. If it's a complex problem it's one that must use an emergent approach. We can not define the solution up front.
Is there a solution - yes. That's what puts it into the Complex (vs Chaos) space.
Complex problems DO NOT have a clear answer. We CAN NOT do the design up front to produce a piece of software reflective of a solution.
The solution is one that can only be discovered by emergent design of the application through itterative steps.
The book says...
... I think it's saying that complex problems can't have simple solutions...
Which... OK... But I also disagree. When you ruthlessly refactor your code and practice emergent design... the result is simpler. Maybe not "simple". It's going to be a simpler implementation that has clear responsibilities and associations for the domain.
The book has 2 sentences for this one. I feel it's ... I don't know. Dumb?
Sorry this is a terrible post... it's a terrible principle in the book.