Level 6 · Lesson 12
Common Strategy
Killers
Why good strategies fail in practice. 10 killers that destroy working edges — and how to defend against each one.
First — Why This Matters
🔍 Death by a Thousand Cuts
Most strategies do not die in a dramatic explosion. They die slowly — a curve-fitted parameter here, a broken rule there, a missed regime shift, a few extra trades outside kill zones. Each one is small. Together, they bleed your edge dry until a profitable strategy becomes a breakeven strategy, then a losing one.
The worst part: you often do not notice until it is too late. Your win rate drops from 52% to 46% over 3 months and you blame the market. In reality, YOU changed — the market is the same. This lesson identifies the 10 killers so you can defend against each one before they compound.
🔎 REAL SCENARIO
A prop firm analysed 3,200 funded traders over 18 months. Of those who eventually failed, 72% had profitable strategies on entry. They did not fail because their strategy was bad — they failed because they gradually destroyed their own edge through the killers in this lesson. The strategy survived. The trader did not.
01 — The Slow Death
How a Healthy Edge Decays
Watch a profitable equity curve gradually erode as each killer takes its toll. The strategy was never broken — the trader broke it.
02 — Threat Ranking
10 Killers by Severity
03 — The 10 Killers
Each One Explained + The Fix
04 — The Compound Effect
Killers Multiply, Not Add
Each killer alone reduces your edge by 5-15%. But they COMPOUND. Two killers do not cost 20% — they cost 25-30%. Three killers cost 40-50%. By the time four killers are active, your +£40 EV edge is zero or negative.
| Active Killers | Edge Remaining | £40 EV becomes |
|---|---|---|
| 0 | 100% | £40 |
| 1 | 85-90% | £34-36 |
| 2 | 70-75% | £28-30 |
| 3 | 50-60% | £20-24 |
| 4 | 30-40% | £12-16 |
| 5+ | 0-20% | £0-8 (likely negative after costs) |
💡 The Leaky Bucket Analogy: Your edge is water flowing into a bucket. Each killer is a hole. One small hole is manageable. Five holes and the bucket empties faster than it fills — even though water (edge) is still flowing in.
05 — Strategy Health Diagnostic
Is YOUR Strategy Under Attack?
Answer honestly about your current trading. See which killers are active.
Did you change any strategy parameters recently?
Has the market regime changed since your strategy last worked?
Have you broken your rules in the last 10 trades?
How many trades in your current sample?
Do you account for spread and commission in results?
How many strategies have you tried in the last 3 months?
Do you journal and review weekly?
Do you trade outside your asset's active sessions?
06 — The Defence Playbook
5 Rules That Block Most Killers
1. Use standard parameters. RSI 30, EMA 21/50/200, 1% risk. Round numbers that work across a range. Kills curve-fitting.
2. Add a regime filter. ADX > 25 for trend strategies, range boundaries for range strategies. Know WHEN your strategy applies. Kills regime blindness.
3. Journal every trade + weekly review. Catches emotional rule-breaking, reveals session leaks, quantifies every killer. The diagnostic system.
4. 100-trade minimum before ANY judgement. Prevents strategy hopping and sample-size delusion. Commit to the data.
5. Calculate net EV (after costs) before going live. If gross EV minus spread minus commission minus estimated mistakes is still positive, the strategy is viable. If not, fix it first.
07 — When to ACTUALLY Change
Legitimate vs Emotional Reasons
Legitimate reasons to change:
Net EV is negative over 100+ live trades (after costs). The market structure has fundamentally changed (new regulations, new instruments). Your lifestyle has changed and the strategy no longer fits your schedule. The journal reveals a specific, quantified problem that a rule change would fix.
Emotional reasons (NOT valid):
"I lost 5 trades in a row." "My friend makes more money with a different strategy." "I saw a YouTube video about a better method." "I am bored with my current strategy." "The market is broken." "I think I can do better."
08 — The Meta-Mistake
Knowing the Killers but Not Defending
The biggest irony: most traders who read this lesson will nod at every killer, agree with every fix, and then continue doing the same things. Knowledge without implementation is entertainment, not education.
Reading about curve-fitting does not prevent it. Having written rules with standard parameters does.
Knowing about regime changes does not help. Having an ADX filter that blocks trades in the wrong regime does.
Understanding emotional rule-breaking does not stop it. A pre-trade checklist and a journal that tracks rule compliance does.
💡 The Implementation Test: For each of the 10 killers, write down your SPECIFIC defence. If you cannot write a concrete defence (not "I will try harder" but "I use ADX > 25 as a regime filter"), that killer is currently active in your trading.
09 — Cheat Sheet
Killer Quick Reference
CRITICAL = Curve-fitting, Regime blindness, Emotional rule-breaking. Fix these FIRST.
HIGH = Strategy hopping, Ignoring costs, Insufficient sample size. Fix after the criticals.
MEDIUM = No journal, Moving stops, Wrong sizing. Important but less urgent.
DEFENCE = Standard params + Regime filter + Journal + 100-trade rule + Net EV calculation.
COMPOUND = Each killer reduces edge 5-15%. 3+ killers active = edge near zero. Fix the biggest leak first.
10 — Test Your Understanding
Strategy Killer Game
5 scenarios. Identify the killer and the fix.
A trader's backtest shows 54% WR with 1:2 R:R over 120 trades. He goes live and after 60 trades: 44% WR, 1:1.6 R:R. He decides the strategy is "broken" and starts looking for a new one. What strategy killer is at work?
11 — Knowledge Check
Final Quiz — 8 Questions
Question 1 of 8
What is the MOST dangerous strategy killer?
Question 2 of 8
A strategy worked for 4 months then lost money for 6 weeks. What should you check FIRST?
Question 3 of 8
A trader changes 4 parameters of his strategy and results improve. Can he trust the improvement?
Question 4 of 8
How does edge erosion typically affect backtest-to-live performance?
Question 5 of 8
What is "strategy hopping" and why is it destructive?
Question 6 of 8
A strategy has +£30 EV in backtest. After adding commission (£4) and spread (£6), the net EV is +£20. Is this strategy viable?
Question 7 of 8
What is the correct response when you detect regime change?
Question 8 of 8
Which of these is NOT a strategy killer?