In brief
In a restaurant, the voice you want to hear mixes with other voices, music and dishes. The brain must pick out the right sound and fill in unclear parts.
What it can mean in daily life
Even a mild change in hearing can make this tiring. Hearing aids can help, but they cannot always separate one voice perfectly from every other sound.
Next steps
Try sitting close to the person, choosing a quieter place and asking them to speak clearly at a natural pace.