Stock market returns will tend to exceed inflation. Salary may not. It's quite possible for inflation to make your salary shrink in real terms, making it no longer worth working if you can afford to retire.
There is absolutely no guarantee that stock market returns exceed inflation. The big US indices have for the last few decades, but they're extreme outliers.
You'd expect this to happen with a couple of reasonable assumptions, like stock prices being somewhat based on real value most of the time, no wide-scale long-term economic collapse, and new companies replacing incumbents over many years rather than very quickly. If the real value of a company stays constant, then the stock price should, on average over the long term, rise at a pace that matches inflation.