If you're retired, counting on a 100% stick portfolio is extremely risky, unless you have so much that losing half your portfolio in a single year wouldn't move the needle.

Imagine you just retired with the $1.66M you assumed, and stocks lose 50% that year. Everything you have is in those stocks, so now you have to take the same $50k out of $783k as you planned.

Now, even if stocks double the following year, you're at $1.47M, and that's without counting any inflation. Imagining 3% inflation, your portfolio is now worth $1.42M in real terms.

If you could have barely lived off a $1.66M portfolio, you certainly can't do the same off $1.42M.

That's why Bengen's research in the 1990s used a 50/50 stock/bond portfolio to come up with the 4% rule. When you're retired, you can't afford to spend down stocks when they crash.