For these trust funds we work to link stock selections with long-term thinking. These portfolios start when the beneficiary is 11 or so years old so they have a long time horizon.
With that, there are times that it is wise to sell. If you believe that a stock has been part of a huge run-up and gains are not sustainable, you should sell. We sold a number of stocks in 2007 when valuations were insanely high (such as China Mobile (CHL), which peaked near $100 in 2007-8 and now is settled back in around $50 / share) and many of them have not recovered back to those levels. Unfortunately, we re-invested the proceeds into new stocks which promptly went down with the rest of the market but it still was the right thing to do.
On the other hand, some stocks seem to get permanently impaired or on a downward spiral from which they never recovered. We bought Nokia (NOK) and then sold at a loss – and the stock has kept dropping since, damaged by their dismal position in the smart phone market. We also did the same with Cemex (CX) which also had a high near $40 in the 2007-8 time frame but has settled to around $10 / share.
It is hard to know when to capitulate, and when to hold on to wait for the rebound. Urban Outfitters (URBN) was selected because it had low debt and seemed well run – until they had a bad earnings report and the stock tanked. We held onto it for over a year after it had lost about a third of its value, and then a lot of their top management resigned. Yet recently it came back and is now above its original purchase price. Other stocks that we waited on until they came back include Comcast (CMSCA) and Ebay (EBAY). On the other hand, we are still waiting for recovery on Canon (CAJ), Riverbed (RVBD), WYNN, Exelon (EXC), and Alcoa (AA). I am bullish EXC in the long term as well as RVBD; I think there is hope for CAJ because they are well run; and watching WYNN and AA.