According to the latest Nall Report, published by AOPA...

Weather was the most deadly accident cause.
In 2001, it resulted in a fatality rate of 56.5 percent for single-engine fixed-gear aircraft, 89.5 percent of retractable-gear aircraft, and 100 percent of multiengine aircraft.
While complex aircraft fly longer distances and encounter more weather, single-engine fixed-gear aircraft continue to be involved in weather accidents. One factor is continued VFR flight into IMC. Accidents that result from this type of flight have a fatality rate of 90 percent.

Also from the Nall Report...

The Boeing Commercial Airplane Company, studying accidents of transport-category aircraft, found that most result from a sequence of events rather than a single catastrophic event. Their research identified as many as 20 events in a single flight that directly influenced the accident. The NTSB uses a similar method to break down each accident into “occurrences.”

Note: These "events" are what some call "links" in the error chain.

A pilot's attitude can be his or her most valuable asset, or his or her greatest liability. Every decision made is influenced by attitude. It's no news flash that human factors are the number one cause of all aircraft accidents. But the implications of this fact are sobering: this week, somewhere, an aircraft will crash and people will die. If that aircraft had a different pilot with a different attitude, that aircraft might not crash, and those people might not die.

Note: I did not say a better pilot; I said a pilot with a different attitude. Of course, a better attitude would make him or her a better pilot, but not in the sense we often think of when we say "better pilot" (like being a "good stick"). The attitude we're talking about would include characteristics like conservative, cautious, inquisitive, proactive, pragmatic, professional, decisive, and informed, to name a few.

Pilots need to realize that most of the tools needed to be a good, exceptionally safe pilot, are within them, right this minute. To access these tools a pilot need only make a commitment to being professional. Not a professional in the sense of someone who is paid. There are plenty of pilots who are paid to fly airplanes but are not very professional. I mean professional in the sense of an attitude and a demeanor that is real and uncompromising. Now, it is not uncommon for people to occasionally drive over the speed limit, or continue driving their car in very heavy rain or snow. Both of these activities elevate the risk associated with driving. But, if we as pilots carry this same attitude into the cockpit, we are not going to last long. A plane ride should not resemble a weekend boat ride. It is not the same thing. Aviation is very unforgiving to those who push the limits.

Pilots should make a commitment to constantly improve themselves. This includes spending some time reading about human factors in flight. Before every flight, a pilot should be able to recognize the outside factors (stress, money, commitments, etc...) that will effect their decisions. Recognize when your day is starting to resemble something you read in an NTSB report and with the authority as the Captain and the demeanor of a professional, say, "we're scrubbed."

Many flights have a purpose other than just to "go fly." When the purpose is just to "go fly," it's sometimes easier to keep the flight in perspective. If, say, the weather is terrible, you know it's just not going to be any fun to fly today. So why bother? When we use the aircraft as a transportation tool, however, weighing that decision can become more and more difficult. So much of the time, the factors that effect our decisions have nothing to do with aviation; they have to do with life and a million different variables.
This section of Flight Analysis includes a short training scenario. It only takes about 10 minutes, and it's just for fun. The purpose is not to show right from wrong, but instead to highlight the fact that many decisions are not aviation-based. Take from it what you will. Click on the picture below to begin training.

History of flight:
The pilot and passenger flew to the Wilkes Barre Scranton International Airport (AVP), Wilkes Barre, Pennsylvania, from Northampton, which was the airplane's home airport. After departing Wilkes Barre for the flight home, the pilot made an unscheduled stop at Ellenville.

After making an unscheduled stop due to weather, the airplane departed on the accident flight. Once airborne, the airplane proceeded to the north towards mountainous terrain. No information regarding the route of flight was obtained for the airplane after it left the airport environment. The wreckage was located approximately 140 feet from the top of a 1,220-foot ridgeline, and about 10 miles east of the departure airport. The start of the debris path was marked by freshly broken tree branches at the top of a 60-foot tree. A path of freshly broken branches approximately 340 feet long connected the initial tree strikes to the main wreckage. The path was on a magnetic heading of 140 degrees, and had a down angle of approximately 2 degrees. At the time of the accident, the ridge was obscured by clouds, and the visibility was approximately 500 feet. Examination of the wreckage revealed no preimpact failures or malfunctions with either the airframe or engine.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot-in-command's failure to maintain sufficient altitude while maneuvering in a mountainous area, which resulted in a collision with terrain. Factors in the accident were, mountainous terrain, clouds, and the pilot's decision to continue the flight in deteriorating weather.