Who this entry is for — "Nothing is perfect — there are pitfalls." The method is probabilistic, not infallible — and when it goes wrong, it goes wrong for three precise reasons. Knowing them in advance turns the unexpected into procedure.
Source: J. M. Hurst, The Profit Magic of Stock Transaction Timing, Prentice-Hall, 1970 — Chapter 10, § Why the Unexpected Occurs (pp. 158–159).
Prerequisites
The cyclic cut-loss and trailing loss levels (Ch. 5), triangles (Ch. 3), the half-span and full-span averages (Ch. 6).
The three causes, with remedies
1 · The sudden fundamental shock
The cause to guard against most: the totally unpredictable fundamental factor that hits a specific stock without warning. It has nothing to do with the smooth, long-term push characterizing 75% of price motion: this is what throws investors into a selling panic, or has them flooding the issue with buy orders no matter the price.
The procedure is already in the method: if the shock aids your position, shift immediately to terminal sell criteria; if it works against you, "let your trailing loss level signals be your guide". It does not happen often — and when it does, proceed as described and put your funds to work in another issue.
2 · Magnitude drying up
The second cause is the unpredictability of your trading cycle's magnitude-duration fluctuation. The main defence: enough past data — the variations are not sudden, and a longer window warns you when a cycle's magnitude is due to dry up (the book recommends Standard & Poor's Trendlines: nearly a thousand issues on weekly charts covering about four years).
And never overlook the signs of its arrival:
- constant-width envelopes that no longer fill;
- the formation of triangles, coils, wedges and diamonds, in the manner of Fig. III-9.
When it happens on components shorter than your trading cycle it can be a great aid (it is the triangle resolving); when it happens on the trading cycle itself, "trouble is at hand" and the issue should be temporarily avoided. Here too: rare — and in any case the trailing loss levels protect against major loss.
3 · The overlooked long components
The third source of difficulty: overlooking the status of longer-term components. Sometimes they are just emerging from a magnitude-duration crossover and cannot be seen in past data; at other times the culprit is an inadequate span of past history. The guard: always keep all the model's components clearly in mind and account for as many as practical in the analysis. "If doubt exists, resort to the computational methods of Chapter Six — or select another issue on which to trade."
Summary card
| Cause | Signs | Remedy |
|---|---|---|
| Fundamental shock on the issue | Panic or order flood, without warning | Aiding → terminal sell; against → TLL; then another issue |
| MD fluctuation on the trading cycle | Envelopes failing to fill; triangles/coils | More history in the data; avoid the issue for a while |
| Overlooked long components | Magnitude crossover; short data window | All components in mind; Ch. 6; or another issue |
Warning — The chapter is blunt: in all three cases "trailing loss levels will protect you against major loss". The safety net is not an extra: it is why these mishaps stay incidents rather than disasters. The rest of the chapter — the psychological enemy — is in the six barriers.
Links
- The psychological barriers — the other half of Ch. 10
- Cyclic cut-loss and trailing and take-profit — the safety net
- Triangles — MD fluctuation up close
- Half-span and full-span — the methods of doubt
- Hurst tradition — chapter index