Dear David, I am relatively new to being an active investor. In the past I have watched my pension fund, managed by professionals, take enormous hits.
One of the issues I struggle most with is the idea of a long term portfolio.
The RDSB chart shows the share peaked at about 2600 and has recently dropped to a low of 1260.
You comment that it has a good dividend. If I am not mistaken the dividend is likely to be set in relation to the share price, so while it may not decline in percentage it will decline in actual amount.
So, in theory you (or I for similar shares) would be better to sell as the decline becomes apparent. 
In an era of volatility is the long term portfolio an outdated concept, provided you have an understanding of the costs of moving in and out of a share. Regards Anthony

David Fuller's view

Thanks for an email of general interest on the oldest debate among stock market investors.

My first comment would be to follow your instincts, including a degree of experimentation from time to time, if that suits you. 

Because stock markets are volatile, every investor will take some big hits on occasion, although that is never our intention.  Active managers will have their own rules for selling or at least reducing positions. That will prove effective in a big selloff, but include a number of whipsaws in choppy markets which are a more frequent occurrence. 

Buy-low-sell-high

A helpful tactic which I have long advocated, is to lighten positions in an uptrend which is clearly becoming overextended relative to its rising 200-day (40-week) MA, because that rate of advance will not be sustainable beyond the short, or at most, medium-term.  You may choose to repurchase if it returns to the MA in an order fashion, or hold off if you suspect top formation development is underway.  Personally, I have not done this often enough – it is too easy to procrastinate, although I hope to improve on that going forward.  

Conversely, if a share you like because of its quality, earnings, dividend or cyclicality is temporarily out of favour, it may be a good idea to purchase more following a setback.

Re Royal Dutch Shell B, it has long had an attractive yield, and if it can maintain the dividend in a downturn, that yield becomes more attractive as the share falls.  One is also paid for one’s patience. 

Lastly, eras of high volatility can persist for a long time, although they tend to be finite.  Moreover, they are eventually followed by more persistent trends.