Basketball star Shanille O'Keal's team statistician keeps track of the number, $S(N),$ of successful free throws she has made in her first $N$ attempts of the season. Early in the season, $S(N)$ was less than 80% of $N,$ but by the end of the season, $S(N)$ was more than 80% of $N.$ Was there necessarily a moment in between when $S(N)$ was exactly 80% of $N$?
1. Define the function \( S(N) \) as the number of successful free throws made by Shanille O'Keal in her first \( N \) attempts.
2. According to the problem, early in the season, \( S(N) < 0.8N \). This means that for some initial number of attempts \( N_1 \), the success rate is less than 80%.
3. By the end of the season, \( S(N) > 0.8N \). This means that for some later number of attempts \( N_2 \), the success rate is more than 80%.
4. We need to determine if there was necessarily a moment in between when \( S(N) = 0.8N \).

To prove this, we can use the Intermediate Value Theorem (IVT), which states that if a function \( f \) is continuous on a closed interval \([a, b]\) and \( f(a) \) and \( f(b) \) have opposite signs, then there exists at least one \( c \) in the interval \((a, b)\) such that \( f(c) = 0 \).

5. Define the function \( f(N) = S(N) - 0.8N \).
6. Early in the season, \( f(N_1) = S(N_1) - 0.8N_1 < 0 \).
7. By the end of the season, \( f(N_2) = S(N_2) - 0.8N_2 > 0 \).
8. Since \( f(N) \) is a discrete function (it changes in steps of 1 as \( N \) increases), we need to check the values of \( f(N) \) at each integer \( N \) between \( N_1 \) and \( N_2 \).

9. If \( f(N) \) changes from negative to positive, there must be some integer \( N \) where \( f(N) = 0 \). This is because \( f(N) \) is a step function and must pass through zero to change from negative to positive.

10. Therefore, there exists some integer \( N \) such that \( S(N) = 0.8N \).

The final answer is \( \boxed{\text{Yes}} \)