BR disagreement/fallacy

I hear from everyone if your BR gets too low then it's time to play lower stakes. I disagree with this "if your at least a break even player or better". Here is why, you have a BR of 500BB, with that kind of player and BR means you should never go broke, EVER! This will handle any and all variances in your game. So what if you get down even 200BB, you have the BR for that reason and you will get even again. IMO if one has to play lower stakes then they were never a break even player at the stakes in the first place. Can someone explain to me why this wrong?