Do you think the sum of a negative number and a positive number will always be negative?

No, the sum of a negative and a positive is a negative only if the negative number is larger than the positive one. for example:

-5 + 4 = - 1

since negative 5 is larger, and it's negative that's why the answer is negative.

5 + - 4 = 1

since 5 is the larger number, and it's positive, the number is positive.