Unlike the post-GFC era, governments now lack the fiscal and monetary flexibility to cushion every economic shock due to high debt levels. This is forcing global markets to trade on their own fundamentals again, creating volatility and relative value opportunities reminiscent of the pre-2008 era.

There is no universal debt-to-GDP ratio that triggers a crisis. The actual tipping point occurs when investors collectively lose faith and stop buying bonds. This moment is driven by human psychology and expectations, making it impossible to predict with a formula and susceptible to a sudden stampede for the exits.

The CAPE ratio has crossed 40 for only the third time in 150 years. The previous two instances were immediately before the 1929 Great Depression and the 1999 dot-com bust, suggesting extremely negative 10-year returns for stocks.

History shows that markets with a CAPE ratio above 30 combined with high-yield credit spreads below 3% precede periods of poor returns. This rare and dangerous combination was previously seen in 2000, 2007, and 2019, suggesting extreme caution is warranted for U.S. equities.

History shows a strong correlation between extreme national debt and societal breakdown. Countries that sustain a debt-to-GDP ratio over 130% for an extended period (e.g., 18 months) tend to tear themselves apart through civil war or revolution, not external attack.

Historically, the debt-to-GDP ratios of the world's largest economies have moved in unison. As long as this trend continues, a high ratio in one country is less of a crisis because it's a relative problem. The real risk is one nation decoupling with significantly different economic output.

The TWIG acronym (Trade, War, Inflation, Government Intervention) posits that the best investment returns occur with maximum trade, no war, minimal inflation, and limited government intervention. The opposite conditions historically lead to the worst, often negative, returns for investors.

The standard market cap-to-GDP ratio can be adjusted by subtracting US federal debt, assuming the Fed will ultimately monetize it. This "Adjusted Warren Buffett Metric" is now higher than at the peaks of the 2000 tech bubble and 2021, signaling stocks face a terrible risk-reward setup.

To assess true macroeconomic stability amid market noise, investors should monitor four specific signposts: inflation expectations, government debt volatility, U.S. dollar valuation, and credit market stress. As long as these core indicators remain calm, the fundamental case for market strength holds.