Post Hoc Fallacy
The concept of 'post Hoc Fallacy' is a false assumption in which because one event happened before another event, it must have caused the proceeding event. Though, this type of reasoning becomes tempting when the previous behavior seems logically related to the later one, we need to be to be careful because the scientist found a lack of evidence for whether earlier event actually causes the proceeding event (correlation vs. causation). The concepts of Post Hoc Fallacies are usually committed because people are simply not careful enough when they reason. Jumping to a causal conclusion is always easier and faster than actually investigating the phenomenon. When considering examples of Post Hoc fallacy some examples are very plausible to make senses whereas others are not so much reasonable. In most cases, the heauristical conclusion seems far from the reality.

For example, I heard one of my friends who said, " after failing my first two test, I begun to use a pen my mother gave me and I started getting better grade". From this example, we cannot simply conclude that his grandmothers gift is the cause for his improvement because there could be a third factor, because he did really bad on his test he found a new way to study or spent more time studying.
http://www.nizkor.org/features/fallacies/post-hoc.html
Why do you think people show this tendency? What are some possible other examples. What is your link and why should we go there (also use the link function)?