Backtest Pitfalls: Overfitting & Survivorship Bias

📈 Sign up today at https://public.com/traderlion and earn a 1% uncapped match when you transfer your investments.📚 Order The Trader's Handbook Here: https://go.traderlion.com/uilGP📘 Get your FREE 115-page Ultimate Trading Guide: https://go.traderlion.com/uihtc🔍 Next-Generation Stock Screener: https://go.traderlion.com/uihtjTy Rajnus of Rajnus Capital returned an incredible 382% in the 2025 US Investing Championship — all short trades, zero losing months. A day trader specializing in nano cap and micro cap stocks, Ty brings a fully systematic, backtesting-first approach to the short side that's unlike anything we've featured before on the TraderLion podcast.In this episode, Ty breaks down his entire process from the ground up: how he discovered short selling after starting with a $2,000 gift from his grandfather, why he dropped out of engineering school to trade full time from a camp trailer, and the data-driven methodology that's produced remarkably consistent 200%+ returns for three consecutive years. He walks through his backtesting framework in Excel, explains how he identifies overextended penny stocks primed for a reversal, and reveals how changes in volume and liquidity create his highest-conviction entries.Ty also shares his best and worst trades of 2025, his compounding position sizing strategy, the terrifying reality of T12 halts and overnight holding risk, and why he believes the most powerful trading fund would combine five uncorrelated strategies. Whether you're interested in short selling, systematic trading, or simply building a more data-driven approach to the markets, this one is packed with insights.

This isn't just theory — this is a proven, data-backed system delivering consistent results year after year.Enjoy!

- The TraderLion Team

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Timestamps:0:00 - Welcome & Ty Rajnus Introduction4:09 - How Ty Got Started in the Markets8:00 - Switching from Long to Short Side9:57 - Engineering Background & Dropping Out of College12:05 - COVID-Era Observations & Finding His Edge15:38 - Defining His Style: Short Only, Systematic, Day Trading19:10 - 2025 Results: 382% Return, Zero Losing Months23:07 - USIC Metrics: 238 Trades, 66% Win Rate27:43 - Risk Management & Backtested Max Drawdown Sizing33:31 - Building a Strategy from First Principles36:11 - The Core of Backtesting: Removing Emotions & Proving Edge39:13 - Data Collection & Excel Walkthrough43:55 - #1 Factor: Overextension to the Upside48:21 - Locating Shares & Broker Selection52:14 - The Zero DTE SPX Options Strategy59:48 - Key Niche Components: Dilution, Parabolic Action, Liquidity1:05:53 - Volume & Liquidity Transitions as Entry Signals1:11:32 - Risk Management & Wide Stops for Short Sellers1:20:09 - Dealing with Halts: LUDP, T12 & Scaling Out1:30:14 - Overnight Holding Risk: The $5 to $125 Lesson1:34:51 - Compounding Position Sizing Strategy1:37:03 - Best Trade of 2025: CWD Crypto Treasury Play1:46:36 - Worst Trade of 2025: Zero DTE Blown Out During Tariffs1:48:47 - Mindset: Execution Over Income & Having a Side Hustle1:52:10 - Contrarian Mindset & When Friends Text About Stocks1:56:01 - Jim Simons, Medallion Fund & Multi-Strategy Vision1:58:05 - Day-to-Day Pre-Market Routine & Execution Process2:01:27 - Closing Advice for Traders