"To miss out on" (something) means to lose the chance to do something or obtain something. Te vas a perder una gran oportunidad.

You lost the opportunity to go eat ice cream=You missed out on getting ice cream. You missed out on a great wedding=Because you were unable/unwilling to go to the wedding, you did not enjoy the positive experience that I enjoyed. Missed out implies that because one either could not do or did not do something, he did not enjoy a positive experience.