A life, even one full of meaning, performing all duties, fulfilling all obligations to family and friends and society and even the human species as a whole, if deprived of intrinsic interest, is still a life not worth living by itself. You will still have difficulty getting out of bed every morning.
By intrinsic interest I do not mean material or monetary interest, I mean what you are interested in, naturally and genuinely, and, as in many cases, have a natural gift for. For instance, you really want to be teaching, preaching, playing piano, helping the poor, gardening, doing woodwork, painting, playing with kids, observing nature, traveling, studying economics, leading the community, making a film, climbing a mountain, sweeping the streets, knitting a sweater, or making a doll. You really want to do it.
Whatever you look for leads to it. Even if this desire has been laughed at, or thwarted, you still want it subconsciously. You do not feel alive when not doing it. Maybe you cannot name it, maybe you cannot find it in the National Occupation Codes, but you want it to be your occupation, your life’s work and leisure. It is so vague that sometimes it only becomes clear when you get to the last years of your life, but you are still glad you have found it in this life anyway. The earlier you find it and are able to do it, the luckier you are. You will be seeking it until you find it. You will be searching your soul, this world, the known and the unknown fields, the trodden and untrodden paths, the recognized and unrecognized skills, different places, different peoples, different jobs. Unless you are doing it, you are never truly happy, no matter how high the income is, how sweet the wife and kids are, how beautiful the house is, how widely you have traveled the world, how competent and well-praised you are at your work. No, you will always feel an unnamed part is missing from this life, no matter how you persuade yourself that it is not so, like all other people persuade you, with seemingly solid facts, and by such common standards. You feel guilty for not being happy. This adds to your unhappiness.
A life worth living is a life engaged in the activity of your intrinsic interests and natural talents. You forget time and are immersed in it intensely. Your strengths are being fully used, challenged, and nurtured. You are concentrated, fully engaged, thinking of nothing else. Afterwards you feel not exhaustion, but a deep relaxation and satisfaction, like waking up from a good dream.