Does having mild chickenpox the first time mean you can have it twice?

The immune system: Your immune system and the production of antibodies is a complicated and not exact "process", with ANY illness or vaccine there can be the chance that your body does not produce enough antibodies to identify and prevent a future infection. In short, although rare - you can get chicken pox more than once.

Chickenpox: A second case of chickenpox can happen although very rarely. It is more common if the first case is before one year of age. More likely is herpes zoster which is the reactivation of the varicella virus in one specific area of the body.

Not necessarily: Having the chicken pox, whether mild or severe, generates antibodies to fight the infection. That being said, there are types when a person gets CP but doesn't seroconvert - they don't form the "memory" antibodies against the disease - those individuals can get CP again. It has nothing to do with the severity of their infection, but a general issue with their immune response to that virus.

Rare: There are rare reported individuals who have had it several times.In someone with an impaired immunity, this could happen or someone who receives a bone marrow transplant that does not get the vaccine. It has been seen when infants under a year have a case partially suppressed by maternal antibody, which prevents them from developing their own immunity.Most "recurrent"cases are just misdiagnosis.