The short answer is yes, but I think it is a misguided question. I whole-heartedly agree that short-term stock movement and market direction have a large impact in portfolio performance. The problem is that I do not believe that I have a proclivity to predict either. So I am faced with a decision to either not invest or invest for the long-term. Over the long-term, factors that I have some confidence in predicting have time to manifest. This gives me back the mental capital that I would have spent trying to figure out short-term stock movement and market direction and allows me to deploy that salvaged mental capital into higher return investments like analyzing the cash flow characteristics of an investment or speaking to industry experts.
Here is a perfect example of the problem. A May 19th, 2009 Bloomberg article (http://www.bloomberg.com/apps/news?pid=newsarchive&sid=aW_6Fjnn9JFs) highlights how Daniel Och (Och-Ziff), David Einhorn (Greenlight Capital), John Horseman (Horseman Capital), and Dmitry Balyasny (Balyasny AM) are all skeptical of the recent market rally and Barton Biggs (Traxis) and Byron Wein (Pequot) believe it is time to buy. These are all legendary investors with unlimited analytical resources. How can they have divergent opinions? Because market direction is an immensely complicated equation. Sure, the investors on the right-side of the market call are going to outperform the wrong side, but it may be easier to find good individual investments and let their long-term performance dictate overall returns.