I was at a training event out of state for work a couple weeks ago. In a discussion with a guy from another company (29 years old), the subject of retirement came up. I mentioned that I had a plan to be retired before 40, at which point he asked "what's your number? 1 million? A million dollars doesn't go as far as it used to..."
I informed him my number was 500,000 and that it would allow a little under 20k/year for me to live off of. His response was "There is no way I could survive on only 20k net a year."
I thought 20,000 was actually a lot more than necessary for my wife and myself to live, but I have hobbies that have been deemed "expensive" by some members of this forum, so I gave myself a little more annual spending money than I thought I would need.
It's amazing how many people think retirement is impossible purely because they don't know how wasteful their spending is.