Top mistakes is a per-tag aggregation across the user's closed trades, restricted to tags whose category is `mistake` (the discipline-failure bucket — separate from setup tags, psychology tags, or custom tags).
For each mistake-tag the trader has applied: - sum the net P&L of every trade carrying it - count the trades - compute the avg per-trade P&L
The top three by absolute aggregate cost surface on the card. A trade with two mistake-tags contributes its P&L to BOTH aggregates — we're measuring per-mistake-kind cost, not apportioning a single trade's P&L across labels. (If 'FOMO entry' AND 'no stop' both appear on the same -€100 trade, both aggregates absorb the full -€100. The trader sees both as expensive and decides which intervention to prioritise.)
Tags with positive aggregate are excluded. If the trader labelled three +€50 trades with 'over-sized', the aggregate is +€150 and the tag drops out of the top-3 — that's not an expensive mistake to fix, that's a mis-labelled set of profitable trades. Card stays silent if every mistake-tag the user has applied netted positive (no expensive mistake to surface).
Across the analysis window, 22 trades carry at least one mistake-tag. Aggregations: 'no stop' on 6 trades = -€480 total. 'FOMO entry' on 8 trades = -€340 total. 'over-sized' on 4 trades = -€220 total. 'broke plan' on 3 trades = -€90 total. Total mistake cost: -€1,130.
How to use the card:
The top entry is the single most expensive mistake category in your trading right now. That's the one that gets a journal rule. The runner-ups are noted and re-checked monthly — if eliminating #1 leaves them as the new #1, fix that next.
Why per-tag aggregation, not per-tag count. A 'no stop' tag on 1 trade that lost €500 is more expensive than 'FOMO entry' on 10 trades that lost €30 each (€500 vs €300). Count alone would surface FOMO; the aggregate gets the priority right. The avg-per-trade column is shown so the trader can also see the per-incident severity.
Why a single trade contributes to multiple tags. If a trade has both 'FOMO entry' AND 'no stop', both behaviours contributed to the loss. Apportioning 50/50 would let the trader rationalise away one of them. Counting full attribution to both correctly answers: 'every time I FOMO, what's the average cost' — and FOMO often co-occurs with no-stop, so both numbers are inflated, which is HONEST about the entanglement.
The discipline-elimination math. A trader who eliminates a -€500/quarter mistake by writing a single journal rule clears 4×€500 = €2,000/year of pure friction. Compounding into the equity curve is the entire point of mistake-analysis: it's the highest-leverage trader-improvement work, far beyond strategy-tweaking.
Limitations.
- Depends on tagging discipline. If the trader doesn't tag mistakes, the detector has nothing to surface. Card stays silent below MIN_TAGGED_TRADES.
- Trader-defined names. 'FOMO entry' and 'fomo' are different tags. Encourage tag-name normalisation in the trade-detail UI before this card grows useful for cross-user analysis (post-launch).
- No co-occurrence here. That's TRA-237's job (Mistake-pair co-occurrence). This detector deliberately stays one-dimensional.
Tier: Pro. Wave 6 (Mistake Analysis) opens with this — followed by frequency-over-time (TRA-236), pair co-occurrence (TRA-237), and mistake-free streak (TRA-238).
How to read the card:
1. Hero (left) — the worst single mistake's name + total cost. The number that hurts. 2. Breakdown table — the top 3 by aggregate cost, with count + total + avg per trade. Read top-down. 3. Hint line — total mistake cost across all flagged categories, plus the discipline-elimination prompt.
Re-look frequency: monthly. Mistake patterns stabilise over months, not days; the card is most actionable at the end of a trading month or quarter when reviewing the journal.
Tier: Pro.