George A. Miller published "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information" in 1956 and is one of the most highly cited papers in psychology. It supposedly argues that the number of objects an average human can hold in working memory is 7 ± 2. This is frequently referred to as Miller's Law.
I've learned this in school as well, and I often use the magic number seven when it comes to grouping of elements in more logical units. However recent research question Miller's Law stating that the correct number a human being can hold in working memory is three or four. In my daily life, I can see that this is more likely. When I go shopping, I need to write a shopping list if there are more than four things I need to buy and by this not forget what it was I'm supposed to buy. One could argue that my working memory is worse than average, but I would never agree to such a statement.
But the question remains and is puzzling my mind... Is The magical number 7 still valid?
 Wikipedia article on Miller's Law
 Jeanne Farrington EdD, "Seven plus or minus two"