Co-Google founder Sergey Brin’s decision to shift his base out of California ahead of a proposed billionaire tax is not a curiosity.

It’s a case study.

People like to frame these moves as political statements or ideological gestures. They are neither. They are rational responses to incentives.

Capital, especially at the very top end, is highly mobile, and it tends to move early, not late.

California’s proposal is straightforward on paper: a one-off 5% levy on individuals with net worth above $1 billion, applied to a wide range of assets, including businesses and intellectual property.

The twist is the retroactive element. It would apply to those who were residents at the start of 2026. That detail alone tells you everything you need to know about the direction of travel.

If you signal that the rules can reach backwards, investors start thinking about how far forward they need to step.

Brin’s relocation to Nevada, along with the quiet restructuring of assets and entities, reflects that thinking. It’s not a reaction to a tax being implemented, rather it’s a reaction to the expectation that it might be.

Supporters of wealth taxes argue that they are a necessary correction. A way to address inequality and fund public services. The political appeal is obvious, but the economic record is less encouraging.

France spent decades experimenting with a wealth tax. It raised revenue, but it also encouraged a steady outflow of high-net-worth individuals and the capital they controlled. By the time it was scrapped in 2017, policymakers had already concluded that the broader economic cost outweighed the fiscal benefit.

Sweden abandoned its wealth tax in 2007 for similar reasons. Germany stepped back earlier. Denmark and the Netherlands have either diluted or restructured their approaches. The pattern is consistent enough to be instructive.

Wealth taxes tend to look effective in theory and underperform in practice once behaviour adjusts.

This behavioural response is the part that is often underestimated. Wealth is not a fixed base. It is a set of decisions. Where to live, where to invest, where to hold assets. Change the incentives around those decisions and the outcome shifts.

California is not operating in isolation. It sits in a competitive landscape. Nevada, Texas, and Florida are all offering lower tax burdens and fewer complications. Relocating across state lines is not the same as leaving a continent. The friction is low. The incentives are clear.

Once movement starts, it rarely happens in isolation. One high-profile relocation prompts others to review their own position. Advisory firms run the numbers, boards ask questions, and the conversation shifts from whether to move to when.

There is also a second layer of impact that receives less attention. When capital leaves, it takes more than tax revenue with it. Investment decisions change, early-stage funding becomes more selective, and, of course, hiring plans are adjusted.

Over time, the ecosystem that supported growth begins to thin out.

Silicon Valley did not develop because of geography alone. It grew because capital, talent, and policy created the right conditions. Alter one of those variables aggressively and the balance changes.

The retroactive element of the California proposal introduces an additional complication. It creates uncertainty about how far policy might stretch in the future. Markets are capable of absorbing higher taxes. They are far less comfortable with unpredictability.

None of this is to argue that governments should ignore inequality or fiscal pressures. It is to recognize that blunt tools aimed at wealth often miss their intended target. Indeed, as I am often quoted as saying, wealth taxes are ‘a masterclass in the law of unintended consequences.’

They generate responses that reduce their effectiveness and create knock-on effects that are difficult to reverse.

The debate is often framed in moral terms. It’s more useful to think about it in behavioural ones. How will those affected respond?

The evidence is not ambiguous. They adjust, restructure, and relocate.

Brin’s comments comparing his experience of leaving the Soviet Union in 1979 to what he sees as a shift in policy direction in California will divide opinion. The comparison itself is less important than the fact that he’s acting on his assessment of risk. So are others.

The assumption that the ultra-wealthy will remain in place, absorbing new taxes without altering their behaviour, has been tested repeatedly. Let me be abundantly clear: it has not held up well.

Wealth taxes rarely fail overnight. They erode gradually. Revenues come in below projections, the tax base narrows, and the policy is modified or abandoned. By that point, some of the capital has already gone.

California has a choice. It can proceed on the basis that this time will be different, or it can take seriously the lessons already learned time and again elsewhere over decades.

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London-born Nigel Green is founder and CEO of deVere Group. Following in his father’s footsteps, he entered the financial services industry as a young adult. After working in the sector for 15 years in London, he subsequently spent several years operating within the international space, before launching deVere in 2002 with a single office in Hong Kong. Today, deVere is one of the world’s largest independent financial advisory organizations, doing business in 100 countries and with more than $12bn under advisement.