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Bonsai Partners Letters & Research Archive

Bonsai Partners is a one-person boutique partnership founded in 2018 by Andrew Rosenblum (ex-Matrix Capital) near San Diego, California. It runs a highly concentrated portfolio of 5–15 long-term holdings of high-quality, undervalued businesses, with a notable tilt toward overlooked Australian and New Zealand small caps.

26 pieces · 2018–2025 · updated every Monday

2025

12-31Bonsai Partners 2H 2025 LetterThis investment letter explains that some companies have a 'hidden moat'—not one big advantage, but many small ones that are hard to copy. Take Wise, a money-transfer company. Its edge isn't a single…→12-01Bonsai Partners Graham & Doddsville Newsletter InterviewThis interview tells the story of Andrew Rosenblum, founder of bonsai_partners. He was obsessed with virtual market trading as a kid, and after graduating during the financial crisis, he emailed his b…→06-30Bonsai Partners 1H 2025 LetterThis report argues that great companies need more than just a 'moat' (a hard-to-copy advantage); they also need 'customer advantage'—the ability to keep customers coming back. Using Amazon and money-t…→

2024

12-31Bonsai Partners 2H 2024 LetterThis investment letter warns against copying popular success patterns (like 'the Uber for X'), because once everyone knows them, prices get too high and future returns shrink. Real '100-baggers' (stoc…→06-30Bonsai Partners 1H 2024 LetterThis investment letter shifts focus from explaining short-term losses (down 3.3% in the first half of 2024 vs. the S&P 500's 15.3% gain) to sharing a lasting idea: look for companies with 'operational…→

2023

12-31Bonsai Partners Q4 2023 LetterThis is Bonsai Partners Fund's Q4 2023 letter. The big change: the manager barely traded this year. He raised the bar for new investments, making it harder to swap stocks, so the portfolio stayed stab…→09-30Bonsai Partners Q3 2023 LetterThis fund letter argues that investors should avoid companies with simple, easy-to-understand businesses because they're often fragile and can't handle unexpected changes. Instead, look for firms with…→06-30Bonsai Partners Q2 2023 LetterThis is Bonsai Partners Fund's Q2 2023 letter. The fund earned 3.3% in the quarter, but since 2018 its annual return is 27.6%—way above the S&P 500's 13%. The key point: U.S. stocks are so expensive t…→03-31Bonsai Partners Q1 2023 LetterThis investment letter argues that instead of trying to predict interest rates or recessions, you should focus on owning companies that can survive tough times. The fund manager shows his own fund bea…→

2022

12-31Bonsai Partners Q4 2022 LetterThis fund letter makes a simple but counterintuitive point: a company survives long-term not because it blocks competitors (like patents or network effects), but because customers genuinely don't want…→09-30Bonsai Partners Q3 2022 LetterThis report explains how Wise, a fintech company, cuts cross-border transfer costs to about 0.6% on average, while traditional banks charge 3% to 5%. The key insight: Wise's advantage isn't just techn…→06-30Bonsai Partners Q2 2022 LetterThis letter from Bonsai Partners explains why they didn't change their investment strategy during the 2022 market crash (war, inflation, rising rates). They see price drops like a spring being compres…→03-31Bonsai Partners Q1 2022 LetterThis is Bonsai Partners Fund's Q1 2022 letter. The fund lost 17.8%, worse than the market, but the manager sees market panic as a chance to buy good companies cheap. He introduces 're-founders': non-f…→

2021

12-31Bonsai Partners Q4 2021 LetterThis investment letter explains why a fund called Bonsai lost 13.7% in 2021 while the US stock market gained 28.7%. The manager says that's normal for a concentrated portfolio—short-term pain for long…→09-30Bonsai Partners Q3 2021 LetterThis letter explains why a fund manager lost 13% in Q3 2021 while the S&P 500 gained 0.6%. The main culprit: Chinese stocks, which crashed after sudden policy changes. The manager doesn't think China…→06-30Bonsai Partners Q2 2021 LetterThis letter argues that 'quality' in investing is often vague and leads to groupthink. The author defines quality as how well a product fits its purpose—like a designer bag being low-quality for hikin…→03-31Bonsai Partners Q1 2021 LetterThis is Bonsai Partners' Q1 2021 investment letter. They discuss three main ideas: First, Redbubble (a platform where designers sell T-shirts and phone cases) saw its stock drop, but the manager think…→

2020

12-31Bonsai Partners Q4 2020 LetterThis letter from a top fund manager explains why he earned 275% in 2020 but warns against overconfidence. His key idea: great investors don't just follow rules—they learn them, then break them like Pi…→09-30Bonsai Partners Q3 2020 LetterThis letter from a fund manager explains why he keeps most of his money in just a few stocks instead of spreading it around. His logic: the big gains come from a small number of ideas, so concentrated…→06-30Bonsai Partners Q2 2020 LetterThis letter explains how a fund called Bonsai made over 100% in the second quarter of 2020, far more than the S&P 500's 20%. The manager says this is a one-off, not normal, because COVID-19 boosted a…→03-31Bonsai Partners Q1 2020 LetterThis piece explains how investment firm Bonsai acted during the 2020 COVID crash. It focuses on a new holding, Genasys, which makes public warning systems (e.g., for natural disasters). Its hardware b…→

2019

12-31Bonsai Partners Q4 2019 LetterThis fund manager letter says they made 56% in 2019, but warn not to expect that every year—they aim for 15-20% annually over 3-5 years. Three key points: First, their biggest holding Redbubble (a pri…→09-30Bonsai Partners Q3 2019 LetterThis is a letter from Bonsai Partners' fund manager to investors. The key message: stocks are generally overpriced now, so even good companies can be bad buys if you pay too much. They'd rather hold c…→06-30Bonsai Partners Q2 2019 LetterThis letter from Bonsai Partners explains why their huge 50% quarterly gain isn't normal. For regular investors, the key takeaway is simple: don't chase short-term wins, and trade less. The fund buys…→03-31Bonsai Partners Q1 2019 LetterThis is a letter from Bonsai Partners explaining why their fund returned only 6.1% in early 2019 while the S&P 500 (a broad US stock index) surged nearly 14%. The reason wasn't bad stock-picking—they…→

2018

12-31Bonsai Partners Q4 2018 LetterThis report covers Bonsai Partners' first quarter (Q4 2018), which lost 17.9% while the market fell 10.4%. The manager focuses on their biggest holding, Aspen Aerogels, which makes aerogel—a super-ins…→