Another way of thinking about it:
80% of the “power” of speech is in the low-frequencies. It is easy to “hear” that people are speaking, especially vowel sounds like “a”, “e”, “i”, “o” or “u” which originate in the chest and throat.
However, 80% of the “understanding” in speech is in the consonants which occur predominantly in the high-frequencies and are produced by the lips and tongue. A good example here are the words “night”, “knife” and “nice”. It may be easy to hear the “ni” sound but more difficult to understand what is being said, especially in a noisy environment (which further masks out the consonant beginnings and endings of words).
Even with a mild loss, the fact that yours is concentrated more in the high-frequencies (very common as we age) means that you might struggle for understanding, especially in the presence of background noise. The QuickSin is designed specifically to test this out and also as a way of demonstrating the difference between hearing without hearing aids and the benefit they do provide when worn by the patient.
Hope this is helpful.