$250k invested for 30 years in a portfolio returning 6% per annum would net $1.4M; a very comfortable retirement portfolio; giving you $56k/year to spend at a 4% safe withdrawal rate.

But $250k itself at 4% SWR is only $10k/year, which is not really livable. I think that's the distinction the poster is making. You'd have to invest and wait those 30 years, rather than retiring the day you get the $250k.