Discretionary Trading

Pure discretionary trading will rely solely on the traders judgement. For example a discretionary trader may spot a particular pattern developing on a chart and decide to enter a trade on that basis. It would be impossible to systemise their trading because it relies on subjective judgements and 'gut' feel.

Mechanical Trading

Pure mechanical trading involves the development of trading rules that cover every situation, from entry to exit and position sizing. The trader is executing a predefined plan. They must however take every trade that the system gives them which can be difficult if the trader begins to 'think' too much!

Both sets of trader are working hard at different times and at different things. The mechanical trader spends time developing a system and does not need to think whilst trading, merely executing a plan. The discretionary trader has to be thinking all the time that they are trading and can suffer from 'information overload'.

Which is best?

The answer is probably a combination of both approaches. Coming to the market with a proven strategy rather than relying on gut instinct is far less stressful and gives the trader more confidence. However the markets are always changing and one trading strategy will not work forever - i.e. the Turtle Traders. Strategies will always need updating.

Many traders will use a mechanical system to generate buy and sell signals but then use discretion, reading the market, to attempt to gain better fill prices.

All successful traders will use some sort of proven trading strategy to begin with but the level of discretion allowed by it will vary. A trader with no plan at all will fail.