There are short-term trading techniques that have an edge. For example, trading breakouts from an opening range can be a successful strategy. I have played with such techniques over the past few months, and have concluded that they are of no help to me as a longer-term trader (which is not to say that I might not give up long-term trading if short-term trading starts to look more profitable!).
The reason is that the success rates of such strategies are low. A good short-term trading strategy may have a success rate well under 50%. Caspar Marney and some of the Market Wizards argue that the kinds of strategies that are resistent to blowing up have this feature: their success is based on the size of winners relative to losers, not a high success rate, and they benefit from market volatility. High-success-rate strategies tend to be those that fade volatility, taking lots of small profits, and thus have a tendency to blow up when there are big moves against them (the small profits don’t outweigh the large losses) or when the strategy stops working for a time.
But the low success rates of robust short-term trading strategies make them unsuitable for timing entries into medium- or long-term trends. When a trend signal is received, be it technical or fundamental, you want to get into it. If you are unhappy with the entry price, you might wait for a pullback. But the signal you are trading is the longer-term one. Trying to improve on the entry is fine — and essential in fuzzy markets like EUR/USD — but trying to time the entry using a robust short-term strategy once a long-term signal has been received will mean missing the trade the majority of the time. The strategy you want for finessing an entry is exactly one of those high-success-rate strategies (generally involving fading short-term moves) that risks a blow-up if traded as a pure strategy on its own.