It is important if someone asks you to remember one of your happiest times to consider not only the question but also the questioner. If the question is asked by someone you love, it is fair to assume that this person hopes to feature in this recollection he has called forth. But you could, if you were wrong and if you had a crooked heart, forget this most obvious and endearing thing and instead speak of a time you were all alone, in the country, with no one wanting a thing from you, not even love. You could say that was your happiest time. And if you did this then telling about this happiest of times would cause the person you want to be happy to be unhappy.