Your anecdote doesn't disprove the scientific effectiveness of vaccines. Because both the Moderna and the Pfizer vaccines require two shots to be at their greatest effectiveness. Since the person you know probably only took the first shot, the vaccine doesn't confer optimal effectiveness, meaning it's entirely possible the person you know got the covid despite having been vaccinated. Even if the person you know took both shots, there is STILL a chance that that person can get covid because both vaccines have an approximate effectiveness of 95%, not 100%, after two shots. So stop being relentlessly obtuse and take your vaccine when it's available to you.