Example 1.3 Divide 4 people into two groups, with at least 1 person in each group, and find the number of different grouping methods.
Solution: Let the required number be $N$. Using Jia, Yi, Bing, and Ding to represent the 4 people, the $N$ grouping methods that satisfy the problem can be divided into the following two categories:
(1) Grouping methods where one group contains only 1 person.
Since the person in the 1-person group can be any one of Jia, Yi, Bing, and Ding, there are 4 grouping methods that belong to this category.
(2) Grouping methods where each of the two groups contains 2 people.
Since the group that Jia is in determines the other group, and the person who is in the same group as Jia can be any one of Yi, Bing, and Ding, there are 3 grouping methods that belong to this category.
By the addition principle, $N=4+3=7$.