Foundations.
The vocabulary.
The concepts everything else stands on: momentum, breadth, volatility, liquidity, Sharpe, drawdown. Answer-first explainers, each tied back to how a live, rules-based system actually uses the idea rather than the textbook abstraction.
Mean reversion vs momentum the two forces every strategy bets on
Momentum says trends persist and mean reversion says extremes snap back. Both are real: they just work on different time horizons. Here is how they fit.
Compounding and volatility drag: why arithmetic and geometric returns differ why arithmetic and geometric returns differ
Arithmetic and geometric returns differ because wealth compounds. Volatility drag is roughly half the variance, and losses cost more than equal gains.
Risk of ruin: the math of how position size kills accounts why a positive-expectancy strategy can still go broke, and why surviving comes before compounding
Risk of ruin is the chance a losing streak drains an account past recovery before its edge compounds. Why position size, not win rate, dominates it.
The Kelly criterion and fractional Kelly
What the Kelly criterion is, how edge-over-odds bet sizing works, why full Kelly is too aggressive, and why practitioners run fractional Kelly.
What is volatility? The most quoted, most misread number in markets.
Volatility is the dispersion of an asset's returns, measured as their standard deviation and annualized by root-time. What it does and does not tell you.
How accurate are quant stock signals?
Accuracy is the wrong question: a good systematic strategy can be right under half the time and still profit. Why expectancy beats hit rate.
Dollar volume. The liquidity gate.
Dollar volume (price times shares) is the liquidity gate: why a signal in a thin stock is untradeable, and how it sets your size and slippage ceilings.
What is overfitting in trading? Brilliant on history, broken live.
Overfitting is tuning a strategy to noise in its backtest, so it looks brilliant on history and fails live. How it sneaks in, and how to catch it.
What is ATR (Average True Range)? A volatility measure, not a direction.
Average True Range (ATR) measures how much a stock typically moves, gaps included. How it's calculated, what it's for, and how Shishin sizes stops with it.
What is the Sortino ratio? The downside-only Sharpe.
Sortino judges return against downside deviation only, not total volatility: the fairer lens for a right-skewed momentum strategy. Plus the Calmar ratio.
What a pre-market scan actually computes.
What a real pre-market scan computes, trend, volatility, momentum, structure, liquidity, and how dozens of measurements become one daily ranked list.
Quant vs discretionary, and where each wins.
Rules vs judgment: where discretionary genuinely wins, where systematic does, and why the real divide is consistency versus adaptability.
Why one strategy can't work in every market.
Markets move through states; a strategy tuned for one fails in another. The case for matching approach to regime, without whipsawing on the turns.
What is alpha (vs beta)? Skill, or just the market?
Beta is the return from cheap market exposure; alpha is the skill-based excess that survives a regression against a benchmark. How to tell the two apart.
What is RSI? The oscillator, not relative strength.
Wilder's 0-100 momentum oscillator: what overbought and oversold really mean, why RSI is not 'relative strength', and why it's context, not a buy trigger.
What is market breadth? What the index level hides.
Market breadth: how many stocks are actually participating in a move, not just a few mega-caps carrying the index. What it reveals, and its limits.
Do stock signals actually work?
Some stock signals work, most don't, and the difference is expectancy net of costs, reproducibility, and whether you actually follow them. How to tell.
What is momentum investing? The anomaly that shouldn't work, and does.
What momentum investing is, why the winners-keep-winning anomaly persists across decades and asset classes, and the regime-turn crash that can undo it.
What a Sharpe of 1, 2, or 3 actually means.
What the Sharpe ratio measures, what a 1 vs 2 vs 3 actually tells you, and the trade-off nobody mentions: a higher Sharpe usually means a lower return.
How breakout setups work, and why most fail.
The anatomy of a breakout, base, pivot, expansion, the mechanic behind the ones that work, and the structural reasons most breakouts fail.
How a stock signal is made, and what it is not.
A trading signal is ranked, rule-based research, not a buy command. How quant signals are scanned, scored, and ranked, and how to spot a real one.