Here is another quote from the same source:
"Analysis of accident data all too often reveals that the situation prior to the accident was “ripe for an accident”. Safety-minded persons may even have been saying that it was just a matter of time before these circumstances led to an accident. When the accident occurs, often healthy, qualified, experienced, motivated and well-equipped personnel were found to have committed errors that triggered the accident. They (and their colleagues) may have committed these errors or unsafe practices many times before without adverse consequences. In addition, some of the unsafe conditions in which they were operating may have been present for years, again without causing an accident. In other words, an element of chance is present."
Jim