Not everyone has to get chickenpox once, some people live their entire lives without the virus and do not get chickenpox, and some people get the chickenpox vaccine to effectively prevent chickenpox infection.
Chickenpox is a respiratory infection caused by varicella-zoster virus infection. Chickenpox is highly contagious and the population is generally susceptible to infection, so most people will be infected with chickenpox after exposure to the varicella-zoster virus and develop chickenpox. However, it is not necessary for everyone to get chickenpox once. Some people are well protected and remain uninfected with the virus throughout their lives, so they can be free of chickenpox.
Some people are actively vaccinated against chickenpox and gain immunity, and even if they are exposed to the varicella-zoster virus, they can remain uninfected or reduce the symptoms of infection.