$75k is a decent salary in most of the US, but if you're in NYC or SF, even his 20% variance (bringing it up to $90k) just isn't enough. If you want to save money, buy a house in the future, and have money to do things, then $120k is minimum in Manhattan, and $90-100k in most of the rest of NYC. Yes, you can live very cheaply in NYC, but at the expense of time; I personally don't want to travel for an hour or more to get to an office, myself.
Saying that a salary is "enough" because that's where happiness flattens out is silly. Most people have no idea how to manage their money, stay out of debt, and prepare for retirement, so they're happy once their salary outstrips their immediate ability to spend.
Saying that a salary is "enough" because that's where happiness flattens out is silly. Most people have no idea how to manage their money, stay out of debt, and prepare for retirement, so they're happy once their salary outstrips their immediate ability to spend.