We shouldn’t use static, unchanging rules because our finances are rarely static and unchanging. I experienced this personally after seeing my savings rate drop from 40% while living in Boston to only 4% during my first year in NYC. My savings rate plummeted because I changed careers and stopped living with roommates when I moved to New York. If I had vowed to always save 20% of my income no matter what, then I would have been absolutely miserable during my first year in NYC. And that’s no way to live. This is why the best savings advice is: save what you can.
