To accept it, you just move on with your life. Find the next thing you should do and do it. The more you dwell, the harder it will be to stop dwelling, so just break the cycle and go do anything else.
You will encounter plenty more people who are insistently wrong. Each one will affect you less than the last.
With jobs, maybe. With careers, especially in STEM, you get lots of exceptions like extremely rewarding but low paying positions in academia, and tech companies that think they can just spend money instead of effort to fix their culture and broken hiring process.