tl;dr:"I’ll talk about things that didn’t make sense to me when I started programming, and now they’re the guiding stars in my sky... it’s not about specific technologies. Technologies come and go. Languages come and go. They can’t be your sky."
tl;dr:Rails is the wrong choice if your team doesn’t want to use it or doesn’t know how, a different framework is better, a specific library you need isn’t Rails-friendly. Noah cites several other reasons, explaining each.