My first US stock was Apple. The reasoning was straightforward: it was Warren Buffett's largest holding and the world's most valuable company at the time. I figured, "If the greatest investor alive trusts this company, maybe I can too." Holding on through the ups and downs paid off well beyond what I expected — it was the first time I truly felt the power of long-term investing.

Fresh off the confidence from Apple, I made my first big mistake. Swept up by bullish semiconductor headlines, I bought SOXL — the 3× leveraged semiconductor ETF. The up days were exhilarating. The down days were brutal. When the index dropped 5%, SOXL erased nearly 15%. After too many nights staring at a screen I couldn't look away from, I sold at a loss. It was a costly but clear lesson: leverage doesn't just amplify gains — it amplifies everything, including the anxiety.

Both experiences led me to the same conclusion: you have to study the market every single day, or the market will study you. After cutting my SOXL position, I started going through US market data daily — and the more I learned, the more convinced I became that disciplined, long-term investing was the only path that made sense. I also realized many Korean retail investors face the same challenge I did: too much noise, not enough signal. marketbrief is my attempt to fix that — one daily summary at a time.