Weight Watchers bloated after stake purchase by Oprah Winfrey

Company's share price has been volatile, erratic, and unnerving

Oprah Winfrey: last October, she took a 10 per cent stake in Weight Watchers when its shares were at a low ebb – prompting them to rocket in value Pic: Getty

Invest in haste, repent at leisure. Amateur investors in the stock market are usually not lacking in common sense, certainly not any more than the population at large. Inexperienced, yes. Impetuous, maybe. Impatient for the quick buck, almost certainly.

The advent of online trading has also probably made impetuousness more common, and is something that the inexperienced or “slightly” experienced investor can be prone to. The absence of a track record to look ...