Outlook
One of the key concepts explored in investment writer Michael Mauboussin’s book, More Than You Know, is the stock market as a ‘complex adaptive system’[1]. The diversity of individual participants generates efficient outcomes in complex systems, that’s to say the collective outperforms the individual. Examples used to prove the power of the collective for decision-making come from nature (social insects such as ants and bees acquiring food or new nests), or from the use of experts by the US Navy to find a lost nuclear bomb (!). The stock market exhibits these characteristics, with multiple information sources, different investment approaches, styles and time horizons generally providing sufficient diversity to yield an efficient market – put another way, “when investors err independently, markets are functionally efficient”.
Markets lose this efficiency if there is a diversity breakdown, which in stock market terms means herding – or “making decisions based on the observations of others, independent of their own knowledge”. While there’s no single barometer for accurately and consistently measuring market phases where “one sentiment becomes dominant”, the respective returns to the momentum and value factors over the past 2 years would suggest some level of dominant sentiment coming into 2025 (e.g., positive on US exceptionalism, tech / AI at the expense of most other things).
A new amplifying factor for this herding has emerged in the past roughly 5 years – the rise of levered and inverse ETFs, particularly in the single stock domain. A recent note we read covered this in more detail[2], but for the uninitiated, “Leveraged ETFs aim to provide a multiple of the daily return of the index they track – for example, a 2x leveraged ETF will seek to deliver twice the daily return of the underlying. … An important characteristic to recognize is that they are designed for short-term trading – due to the way they are structured, their performance can deviate significantly from the underlying index over longer periods.”
Their growth has been staggering, most notably in the Tech & Semiconductor sectors and with single stock levered ETFs developing more recently, dominated by launches for long ETFs rather than short (inverse).

