Why sustainable investing needs fewer hedgehogs and more foxes

In his new book, Osmosis’ Head of Sustainable Investing, Jan Anton van Zanten, challenges conventional thinking and makes the case for a more effective, evidence-based approach to sustainable investing.

Sustainable investing has a bold ambition: to make money work harder for a better world. But are we asking the right questions about how to get there?

For years, the industry has searched for solutions to some of the world’s most complex environmental and social challenges. ESG scores, portfolio decarbonisation, exclusions and impact metrics have all become part of the investment toolkit. Each has its merits. But none, on its own, can solve the challenges sustainable investing is seeking to address. That is the central argument behind Big Money, Better World?

Drawing on scientific research and practical investment experience, Jan Anton explores what sustainable investing can realistically achieve, where conventional approaches fall short, and how investors can make a more meaningful contribution to a sustainable future.

The rise of sustainable investing

Sustainable investing has moved from the margins to the mainstream, driven by two powerful forces.

The first is financial. A changing world is redefining risk and return. Norway’s sovereign wealth fund — the world’s largest investor, holding stakes in nearly 9,000 companies — warned in 2025 that a 3°C rise in global temperatures could erase 19% of its US equity portfolio. When an investor that owns a slice of the entire global economy sounds that alarm, the message is clear: a portfolio built for a stable world is increasingly mismatched with the one we actually inhabit. Anticipating that shift is simply prudent investing.

The second is impact. A growing number of investors — with pension funds like PGGM leading the way — now treat contributing to a better world as an objective in its own right. That is a shift in the logic of investing: from two dimensions, risk and return, to three, adding impact.

The backlash

Yet sustainable investing’s rise has been fiercely contested, from two opposite directions. On one side, critics dismiss it as “woke capitalism” that distracts from the business of generating returns. On the other, critics argue the opposite — that it falls far short of the systemic change the planet needs. Tariq Fancy, BlackRock’s former head of sustainable investing, gave this second critique its sharpest form, calling sustainable investing a “dangerous placebo” that lets people feel they are making a difference while the real work goes undone.

The result is a polarised debate in which asset managers overstate their impact, activists dismiss finance altogether, and politicians reduce it all to culture-war fodder.

Cutting through the noise

Jan Anton’s book takes both arguments seriously, without accepting either as the whole truth.

Its conclusions are sometimes uncomfortable. Many investors who claim to invest sustainably do not. And the real-world impact of sustainable investing is often more limited than its advocates suggest.

To explain what needs to change, Jan Anton turns to an unlikely source: the philosopher Isaiah Berlin and his famous distinction between hedgehogs and foxes. Borrowing from the ancient Greek poet Archilochus, Berlin observed that “a fox knows many things, but a hedgehog knows one big thing.” The hedgehog meets everything with a single defence: curling into a ball of spines. The fox is adaptable, drawing on many tactics.

Much of sustainable investing, the book argues, has fallen into the hedgehog trap: whether the answer is portfolio decarbonisation, ESG integration, or putting a single monetary value on sustainability outcomes – the industry has too often looked for a single solution to problems that are anything but simple.

What the field needs instead is the fox. Unlike the hedgehog’s singular focus, the fox pursues many ideas, embraces complexity, and accepts that sustainability is full of trade-offs. Through the lens of the fox, sustainable investing is grounded in sustainability science and rooted in practice, to seek solutions that work, not just those that sound good.

From good intentions to real impact

This distinction runs throughout the book.

Every topic the book takes on is one the field is grappling with right now: whether “green” funds are as green as they claim, how to tell a genuine sustainability signal from noise, whether sustainable investing actually changes companies and economies, what it means for returns, and how capital can support development where it’s needed most.

For investors these are not abstract questions. They go to the heart of how sustainable investment strategies are designed, implemented and evaluated.

For Jan Anton, they also sit at the intersection of his two professional roles: as a researcher examining whether sustainable investment approaches actually work, and as a practitioner responsible for putting them into practice.

That connection between research and real-world implementation is central to Osmosis’ investment philosophy. The publication of Big Money, Better World? reflects our commitment not just to developing sustainable investment strategies, but to advancing the thinking behind them.

Ultimately, the book is optimistic about the future of sustainable investing. It recognises the limitations of current approaches while making a compelling case for what the field can achieve with better evidence, more sophisticated thinking and a willingness to embrace complexity.

As Jan Anton writes, “potential is not impact.”

Closing that gap is the challenge, and the opportunity, for the next generation of sustainable investing.

What others say

• “Important insights into sustainable investing… an enjoyable and informative book for every investor.”

• —Elroy Dimson, Professor of Finance at the Judge Business School, University of Cambridge

• “Lucid and persuasive… sustainable investors need to evolve from Isaiah Berlin’s famous hedgehogs—who know only one big thing—and become more like adaptable foxes…”

• —Robin Wigglesworth, Author of Trillions and A Fabulous Debt

• “A compelling case for a more nuanced, evidence-based approach… a timely and important contribution to the next phase of the field.”

• —Fiona Reynolds, Former CEO of the UN Principles for Responsible Investment (PRI); President of FAIRR; and Chair of Australian Ethical Super

Big Money, Better World? Rethinking Sustainable Investing for Real Impact is available now from Palgrave Macmillan and major booksellers.

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Important Information

This document was prepared and issued by Osmosis Investment Research Solutions Limited (“OIRS”). OIRS is an affiliate of Osmosis Investment Management UK Limited. Netherlands-based Osmosis Investment Management NL B.V. (“Osmosis NL”) is an affiliate of Osmosis UK and a member of the Osmosis Group of Companies. The book was written by Jan Anton van Zanten in his personal capacity. The views and opinions expressed in the book are his own and do not necessarily represent those of Osmosis NL or any other Osmosis Group company.