Awesome read. I love seeing such letters/articles released 4 years on. Perfect Sequoia investment. Also a great example of a long form business plan (rare these days). It's clear and to the point. No/little explicit marketing BS, written in "plain English", it's not trying to be more complicated than it is. It's intent is to explain the business from top to bottom to a person who knows nothings about it. It covers all the key points including what their assumptions are (and what they dont know).
It's a great example to learn from. Once again, another brilliant investment by Sequoia!