There are elements that I believe may make some sense (i.e. try and be simplistic to a certain extent and keep towards lower costs to facilitate). However, as Mr. Cao indicates, the size of the endowment Warren will leave to his wife can have a rather large impact to the conversation. I have no idea what that amount is, but even given a large equity decline, I would imagine his wife still will not have a large Standard of Living risk. I like the idea behind indexing for sure but to just assume the 90/10 split will work for anyone who is a non-expert investor is neither considering that person's financial situation nor any of their behavior or emotional biases that could derail the "staying the course" mentality. I would guess that she could withstand seeing a 90% decline in the market value of her portfolio and still be more than ok.