The bulls are running wild on Wall Street as investor optimism fuels a relentless rally across equities. The major U.S. stock indices have shattered record after record, propelled by a combination of solid economic data, resilient corporate earnings, and the lingering impacts of low interest rates.

The S&P 500 surged past the 4,500 level for the first time, emboldening traders to bet on further upside despite elevated valuations. The benchmark index has tacked on over 20% already this year, significantly outpacing historical annual average returns.

"There's a lot of froth in this market, but the fear of missing out is more powerful than any valuation concerns right now," said Samantha Jones, Chief Investment Officer at Perception Asset Management. "As long as the economic expansion keeps churning, investors are happy to keep buying even at nosebleed prices."

The relentless bull run is providing a tailwind for equity offerings, margin debt, and other trends typically viewed as signaling euphoria. Companies have rushed to cash in on the frenzy by issuing shares at a breakneck pace. Initial public offering activity has hit its highest levels since the dot-com boom two decades ago.

At the same time, hedge funds have ramped up gross leverage to cyclical highs, allowing them to amplify their bullish bets. Margin debt at major brokerages has also surged as individual investors borrow against their holdings to invest even more.

"The euphoria is palpable across the investment landscape right now," said John Robertson, a veteran trader at Universal Securities. "Whether it's the Reddit mania, crypto craziness, or just classic dumb money euphoria, everyone is incredibly greedy and expecting the good times to keep rolling."

Skeptics warn that the euphoric sentiment leaves the market vulnerable to any shifts in the economic outlook or shifts in monetary policy. Even a whiff of higher interest rates could prove to be the proverbial pin that sends this bull stumbling. However, most investors for now seem content to lean into the fear of missing out.