"And many retail traders don’t know that they have signed terms and conditions with their custodians that allow them to lend the securities in their portfolios to other investors for a fee, none of which ends up in the traders’ accounts, of course."

I beg to differ on the part that you state so firmly that 'of course' brokers will not share the proceeds of securities lending with the asset owners. A 50/50 split of the securities lending fees after out-of-pocket costs is seen regularly and I have also seen a box to check on opening or changing a custody account if you want your securities to be part of a securities lending program. So I also have a problem with the part that many traders would not know about their securities being lent. The rest of the article contains the wise lesson that the long or short party is not over and the game is not won until you are in and out of your positions. Paper profits don't buy anything in the real world unless you take out a loan against your asset (but that too has to be repaid).