Even the shrewdest financial experts make huge money mistakes from time to time—mistakes that can be very costly but that offer important lessons for the future. Bottom Line/Personal asked six money mavens to recall some of the most painful mistakes they have made with their own finances and what lessons can be learned from those mistakes that benefit consumers, savers, borrowers and investors. The experts came up with painful memories that range from a credit card addiction and an emotionally wrenching estate-planning blunder to a scary health insurance stumble and an unfortunate venture involving 17 dairy cows.

Credit card rewards that triggered an addiction. At the beginning of 2000, I started using an American Express card that had a generous cash rewards program. I funneled so much spending through the card that it soon became a game to see how many points I could rack up. Through the end of 2014, I had earned a total of $8,425 in rebates. But over that period, I spent $708,442.45 to get those rewards. And I probably spent 10% more than I should have—a wasted $70,000 that I could have put in my retirement account instead of spending on unnecessary things. Since I never carried a balance and always paid my card in full each month, I reasoned that I was being shrewd and beating the system. Early this year, I sat down and reviewed my purchase history and realized the error of my ways.

Lesson learned: Don’t use rewards points as a justification for spending on items that you don’t need and/or that would stretch you financially.

Source: Curtis Arnold is CEO of CardRatings.com and ­BestPrepaidDebitCards.com. He is author of How You Can Profit from Credit Cards: Using Credit to Improve Your Financial Life and Bottom Line.

A tiny fee that wasted $20,000. Back in 1990, I invested about $25,000 in the Dreyfus Standard & Poor’s 500 stock index fund. I felt smart in choosing a well-respected, broadly diversified mutual fund that charged a much lower expense ratio than actively managed funds. I didn’t do enough research to find out that over the following years, this fund charged between two and 10 times as much as the least expensive S&P 500 fund. And I didn’t realize how much money the higher fees were costing me until a decade later. I eventually switched half of the holdings to another, less expensive fund, but I didn’t shift all of the investment because I was reluctant to pay capital gains taxes on my profits in the Dreyfus fund. This short-sightedness has cost me about $20,000 overall that has gone into Dreyfus’s pocket instead of mine.

Lesson learned: Don’t assume that a fund has the lowest fees until you check similar funds—and realize how costly the difference can be.

Source: Allan S. Roth, CFP, CPA, is principal of Wealth Logic, LLC, a financial advisory firm based in Colorado Springs. He is author of How a Second Grader Beats Wall Street: Golden Rules Any Investor Can Learn.

Why three executors are better than two. In 1992, my mother decided to name my sister and me as co-executors of her will. After Mom died, administering her estate strained my relationship with my sister. We disagreed on various issues and got locked into stalemates that caused some hurt feelings.

Lesson learned: Having three executors with one vote each provides a practical way to break deadlocks. In my own will, my wife and I have named our two children to be the “successor” executors after both my wife and I have died, and we have added a third executor—a trusted family friend—who will be able to break any tie votes and attempt to minimize hurt feelings.

Source: Herbert E. Nass, Esq., is founding partner of Herbert E. Nass & Associates, a New York City law firm specializing in wills, estates, probate and trusts. He is author of The 101 Biggest Estate Planning Mistakes. NassLaw.net

An expensive health insurance bargain. When I began my business a decade ago, I selected a health insurance plan with a monthly premium of $300 and a deductible of $10,000 instead of the $600/$2,000 option. Higher premiums seemed like a waste of money because I rarely went to doctors and figured I could set aside the savings from lower premiums if there ever were an emergency. Within a few months, I needed unexpected prostate surgery. Not only did I have to come up with an enormous sum out-of-pocket, but I also had to endure the stress of this financial hardship while trying to deal with and recover from a frightening and difficult illness.

Lesson learned: Select the most comprehensive health plan available even if you have to make sacrifices to afford it each month. Hospital health-care costs are so high that if you or a family member suffers just one major health crisis, it can make years of paying higher premiums the more economical choice.

Source: Charles B. Inlander is a consumer advocate and health-care consultant based in Fogelsville, Pennsylvania. He was the founding president of the nonprofit People’s Medical Society.

The wrong stove. I had to replace my kitchen stove three years ago. My local Sears did not have a floor model of the exact $1,000 gas range with stainless steel knobs that I wanted, but a salesperson showed me a picture of the one I wanted on the Sears website and I ordered it. When it was delivered, it was not the same as the one pictured. I had neglected to look at the details on the web page. Sears did agree to replace the stove with the one pictured but only ­after a lot of aggravation and expense—I had arranged for a plumber and electrician to be there for installation.

Lesson learned: Retailers often post stock photos that may not exactly match what you think you are buying. Make sure the features and specifications listed are the ones you want and see it in person if at all possible.

Source: Edgar Dworsky is a former Massachusetts assistant attorney general for consumer protection and creator of the consumer information websites ConsumerWorld.org and Mouseprint.org, based in Somerville, Massachusetts.

A misbegotten herd of cows. In 1985, I bought a herd of 17 Holstein dairy cows at public auction for $175,000. I knew nothing about commodity investing and had no interest in becoming a gentleman farmer. But the tax breaks were too good to resist. I put up $20,000 and financed the remainder over five years. In the meantime, I qualified for investment tax credits that gave me $40,000 in initial tax savings. Two years later, Congress eliminated that tax shelter. And it got worse. One of my Holsteins was struck by lightning and killed. Then the US government reduced its support of milk prices and the herd’s value plummeted. I finally sold the cattle at nearly a total loss.

Lesson learned: Many investments, ranging from buying a home to investing in real estate or municipal bonds, offer attractive tax breaks. But reducing your tax bill is just one factor in deciding to invest—and typically not the most crucial one. You need to consider the current value of the investment, your time frame for holding it, the potential for appreciation or loss and what purpose the investment will serve in your portfolio and/or your life.

Source: Edward Mendlowitz, CPA, is a partner at the accounting firm WithumSmith+Brown, New Brunswick, New Jersey. He is author of Getting Your Affairs in Order.