• Rob Mallernee has worked with ultra-high-net-worth families for more than 30 years.
• He said the richest families tend to maintain their wealth with four habits.
• Instilling purpose in the next generation and being frugal are key to preserving wealth, he said.

This as-told-to essay is based on a conversation with Rob Mallernee, 50, who is the CEO of a wealth management software company. He is based in North Carolina. Business Insider has verified his employment. This piece has been edited for length and clarity.

A single brilliant decision might create wealth. But the best way to keep your wealth for 100 years is not one brilliant decision, but hundreds of good decisions over many years.

After more than 30 years working with ultra-high-net-worth families — including most recently as CEO of Eton Solutions — I've seen this pattern firsthand.

The most successful families tend to share these four habits.

Creating the right family culture

The most successful families instil a sense of purpose in the next generations. They foster an environment where the children and grandchildren don't feel entitled, but are motivated to make their own way and add value to the world.

In these families, the subsequent generations don't see the wealth as their own, but as something they steward for the future.

Almost all of our clients do a really great job with that. I'm often amazed at how successful the second and third generations are in building their own careers and achieving something in their lives, despite not needing to because they already have more than enough money.

Treating tax planning as an ongoing process

The second biggest thing these families do to maintain their wealth is being very intentional and thoughtful about expenses and costs.

Typically, one of the highest costs in these situations is taxes, and how you invest your money can be either incredibly tax-efficient or incredibly tax-inefficient.

For example, you could buy an equity fund where the manager is buying and selling all the time. You'd expect a significant proportion of short-term capital gains to be taxed each year, reducing the client's net return.

An alternative is a tax-loss harvesting strategy, where you buy a basket of stocks rather than a mutual fund and sell positions at a loss to offset gains elsewhere. The gross return expectation is the same, but the after-tax returns are significantly higher.

These wealthy families spend a lot of time hiring people to ensure they're not making tax-inefficient decisions. They don't treat tax planning as a one-time exercise but as an ongoing process that considers every financial decision from all perspectives.

Investing long-term

Another common behavior is buying and holding core assets for long periods to reduce taxes and transaction costs.

For example, if they bought a house in Aspen and held onto it for decades, the asset's appreciation is likely to be significant and outweigh the cost of maintaining it over time.

The same principle applies to financial assets. Ultra-high-net-worth individuals with well-planned equity portfolios almost never pay taxes on them because they buy and hold.

If, for example, they need $1 million to buy real estate, they won't sell investments and incur taxes. Instead, they'll borrow against their portfolio or take out a mortgage. Very wealthy people tend to avoid paying cash for their homes because it's not the smartest way to do it.

Being frugal

You may be surprised, but ultra-high-net-worth individuals can be very frugal. While most people assume that they wouldn't worry about the nitty-gritty stuff if they had that much money, I think one way people retain their wealth is by being very frugal and paying attention to costs.

Sometimes that can go to extremes. I could give you several examples of people worth over $100 million asking one of their advisors to look into a cost worth less than $10.

The right way to approach things is to be consistently intentional about all your financial decisions, and it's how wealthy families stay wealthy.