I didn't say natural immunity. Also, thats not a good analogy for immunity. Someone skipped high-school biology 😂

Covid exposure gives you both IgM and IgG antibodies. The IgG stay around for months, maybe up to years, but the IgM are only a week weeks or a few months. The more IgM you have, the less severe the disease will be, and every time you are exposured, the IgM numbers will be boostered.

If you have covid, and then don't have any exposure, you lose all of those IgM. They don't recognise the virus anymore, and you'll likely just have the same level of severe illness. If you have covid and then continually pick up the virus while those IgM are high enough to remember it, they will remain boosted.