Guillermo Rauch is the ceo of vercel. In this tweet, he's effectively saying that the bulk of what his company was built upon (SPAs) is bullshit (zero interest rate phenomenon is a reference to when financial interest rates are very low/zero, as they've been for many years, all sorts of things will seem great and successful because you can borrow money for free. When rates go up, only actually viable projects will survive - as we're seeing in the startup world now).