The Stock Exchange of Thailand (SET) Index has dropped by nearly 5% today in what is described as heavy trading – this is in addition to a fall of just over 2% yesterday (of course, now that the Index is down below 700, even comparatively small changes can represent seemingly large percentage changes). As usual, commentators seem keen to put forward their own reasons for these falls – some will talk about loss of investor confidence following the closing of the Map Ta Phut industrial estate facilities, some talk about concerns over HM the King’s health, some talk about political uncertainty in advance of political rallies to be held this weekend and some will talk of the semi-mythical ‘profit-taking.’ In reality, of course, markets generally move for a whole range of different reasons, including the release of information on specific industries or companies which rarely make the headline news. Evidence increasingly suggests that when several factors coincide in order to create a movement in the same direction (but especially when the movement is downwards), then at some point a herd-like mentality can take over, brokers panic and a more or less random movement turns into an emergent crash. To stop this happening, there are usually ‘circuit breakers’ inserted into the exchanges – for example, trading would be suspended for the rest of the day on the SET if there is a loss of 10% or more in a single day. That gives people time to cool off and return to a more rational frame of mind. On the whole, we might reasonably expect a general decline in the level of the SET (and other regional indices) as the ongoing global financial crisis continues to lead to depressed export markets. This can be exacerbated in Thailand by uncertainty over the future but there are also reasons to feel optimistic about the future economically (although we would probably need a change in those responsible for the economic management of the country). Besides which, the time to sell shares is when prices have gone up and the price to buy them is when prices have gone down.