Week 29 Day 4: Greed in Bull Markets: When Everything Feels Easy

In 1999, day traders quit their jobs because stocks only went up. In 2007, house flippers took on massive debt because real estate only went up. In 2021, teenagers became crypto millionaires because everything only went up. In each case, the 'easy money' period ended abruptly and brutally. The discipline to stay diversified when everything is going up is the discipline that saves you when everything goes down.

Signs you are in a euphoric market (and should be cautious, not aggressive): (1) IPO mania: companies with no revenue are valued at billions. In 2021, over 1,000 IPOs and SPACs launched -- 3x the historical average. (2) New investor surge: brokerage account openings spike. In 2020-2021, 10 million new accounts were opened at Robinhood alone. (3) Leverage expansion: margin debt hits record highs. In late 2021, NYSE margin debt exceeded $900 billion. (4) Meme investing: stocks rise based on social media momentum rather than fundamentals (GameStop, AMC, Bed Bath & Beyond). (5) Innovation worship: 'this technology changes everything' justifies any valuation (AI in 2024 shares some of these characteristics). (6) Experts predicting perpetual bull markets ('Dow 100,000!'). What to do during euphoria: Rebalance on schedule. Your stocks have grown to 85% of your portfolio but your target is 70%? Sell stocks, buy bonds. This is not timing the market -- it is maintaining your risk level. Do not add leverage. Do not chase hot sectors. Do not abandon your plan because it seems too conservative. The boring plan is the one that survives the crash.

Euphoric bull markets exhibit characteristic dynamics modeled by the feedback loop theory of bubbles (Shiller, 2000, 2005). Positive returns generate media coverage, which attracts new investors, whose purchases drive further positive returns -- a self-reinforcing cycle that detaches prices from fundamentals. Goetzmann, Kim, and Shiller (2017) surveyed institutional investors and found that confidence in continued market appreciation peaks just before crashes -- not because institutions are stupid, but because even sophisticated investors succumb to extrapolation bias. The quantitative warning signs map to Greenwood, Shleifer, and You's (2019) bubble model: 60%+ sector appreciation over 2 years, combined with increased issuance (IPOs, SPACs, secondary offerings) and extreme valuations (sector P/E in the top decile historically), predicts a 50%+ probability of a subsequent 40%+ crash. During the 2021 bubble, the SPAC/IPO sector, the cryptocurrency market, and the 'innovation' sector (ARKK) all satisfied these criteria -- and all subsequently crashed 60-80%. For individual portfolio management during euphoric markets, the evidence supports 'countercyclical risk management': tighten rebalancing bands (rebalance when any allocation drifts more than 5% from target rather than 10%), increase the bond/cash allocation by 5-10% as a tactical buffer, and avoid any leverage. This systematic approach captures 90%+ of the bull market upside while providing meaningful protection if the euphoria ends suddenly -- as it historically always does.