This is sure to be a bit controversial, but Jon Kolko makes some great points about design-led vs. lean development in Lean Doesn’t Always Create the Best Products:

And with this, we arrive at perhaps the most important distinction between an empathetic design-led approach and Lean. Lean is fast. Design is slow. Design is more contemplative, reflective, and because it demands systems thinking and marinating in the ambiguity of cultural data, it simply takes longer. The benefit is in producing emotionally sound products: products that people love, not just products people use. Increasingly, people expect more from the products and services they engage with. They expect quality, and use it both as a selection criteria for purchase and as a constraint for sustained use.

I don’t think Lean principles are necessarily in conflict with design principles (there is, after all, a thriving Lean UX movement). But the part that resonates here is the speed pressure that the Lean movement has placed on design activities. All research, prototyping, and graphic design is expected to happen much faster now. Speed is good, but not if it comes at the cost of not truly understanding the problems and user needs you’re designing for. And that’s where Jon’s points are worth taking to heart.