To take a play on the "sold at a loss" theme that Mike just showed up in the previous post... Let's use McDonalds (MCD) as an example.
Here is a chart on Google Finance...
http://www.google.com/finance?q=NYSE:MCD
If you click on the "ALL" choice for the chart -- you'll see many "peaks" -- and also many "valleys". If you'd bought at one of the peaks --- pick any one of the MANY -- but in particular lets say you bought your first batch in 1999 and and sold in early 2003....
It is the lack of long term confidence that would have 'cause you to sell... and now look at how big of a mistake that would have been!
Not all stocks have a chart like this... but that is why you need to have real conviction in your choices TO START WITH... this is why you DO NOT buy some recommendation from the clerk at the grocery store when he gives you his "hot stock tip of the day". That will cost you money every time! Why? Because if it so much as hiccups -- you'll blow out of there at the very first chance and then you'll have taken a real loss.
If -- big IF -- you buy stocks in companies that you like - know - understand - are best of breed... then you'll buy MORE of them as the share price comes down and you'll lower your average cost and you'll sleep well at night with the understanding that in the long run - you'll come out a winner.
Investing -- that's the key term here -- takes time -- it takes commitment -- and most of all it takes some research and confidence that what you've bought is "good stuff".
Another example of this might be housing.
The people that bought houses at the peak -- then bailed or failed... they have a real loss... the guys buying them now... they might suffer for awhile.. they might even question why the hell did they do this... but you've got to believe that the prices will come back. When? Who knows? I have no clue. But I gotta believe that this is "temporary" - it's the scale of temporary vs. the longer term. We won't know what temporary was until we have a longer view, and that view needs time to develop. In the meantime - like a dividend paying stock - the renter of the house will pay towards the mortgage - and eventually you'll have a nice investment even if the price never recovers fully.