Another example of a nasty price gap

If you subscribe to the Mark Douglas theory that in the markets anything can happen, at any time, then you will know and accept the potential effect that sudden or unexpected announcements can have on price of a stock or instrument.

Seemingly you can be comfortably sitting in profit on a trade, even with your trailing stop above your entry price, only for a price gap to occur against you, resulting from the reaction to such an announcement.

It is for this reason why I never take into account open profits for position sizing purposes. A profit or loss on a position is not known until the trade is closed. Open profits can disappear - seemingly overnight with little or no warning, and your trailing stop may be rendered worthless.