Code Explanation Python

I want to find the count of strings in the given array
example if I give an input [the ,the ,the]
the output : {‘the’ : 3}
And I came up with solution below,which is working ,but I could’nt understand the commented line in the code.When we add a string with a number it returns typeError.
Then how is this working.

chr_ = 'the the the'
dit_ = {}

def count_characters(chr_ ='the the power power power nikhil nikhil'):
    count = 1
    list_ = chr_.split()
    for i in list_:
        if not i in dit_:
            dit_[i] = count
            dit_[i] += count       # how does this line help us? 


if there is already a i property in dit_, instead of overwriting the value, the value of count is added to the existing value