If you have ever ordered AirPods or earphones, you would typically receive 3–4 different-sized ear tips with them. This is because everyone's ear canals are unique in shape and size—much like a fingerprint. So brands send you multiple options so that you can try and see which one fits the best.
Earplugs face the same challenge. When they're too large, they won't fit properly in your ear canal and can't provide adequate noise protection. If they're too small, noise can leak through, making them ineffective.
That's why reusable earplugs also come with multiple ear tip sizes. This lets you test different options to find the size that fits best and blocks noise most effectively.
But what about the remaining ear tips you don't use?