[spiralganglion]

If you watch the first two minutes, he explains what the talk is about.

But I'll save you two minutes: Underscore describes itself as affording Functional Programming, but in fact.. it doesn't.

He then goes over several examples of common FP patterns, like currying, composition, and functors, and shows how underscore fails in these regards, and how you can do so much better if a few things were done differently in the library.