An investor will take on more risk only if they expect higher returns in compensation. The idea is a cornerstone of financial theory. Yet look around today and you have to wonder. Risks to growth—whether from fraught geopolitics or vast government borrowing—are becoming ever-more fearsome. Meanwhile, stockmarkets across much of the world are at or within touching distance of record highs. In America and Europe, the extra yield from buying high-risk corporate bonds instead of government debt is close to its narrowest in over a decade. Speculative manias rage around everything from cryptocurrencies and meme stocks to Pokémon cards.