In a cosmic sense, our lives and the existence of all life on Earth is a bit of a paradox - we and the world around us are mind-boggling wondrous contingencies beyond the language of superlatives, improbable almost beyond belief. The paradox comes in the reality that it all amounts to nothing, ultimately, because life has no cosmic meaning and every creature will die, everything else will be destroyed and all that is will vanish forever without a trace.
Which is a polite way of saying life is meaningless, basically, but you're here now so the bright side, REAL wellness thing to do is invent meanings and purposes that promote wellbeing, yours and as many others as possible.
Any discussion about meaning of life invites a distinction between cosmic and terrestrial meaning. Life is meaningless only in the cosmic sense; the opportunities for finding meaning comes in the second kind of meaning, to be discussed next.
Cosmic meaning is meaning from the perspective of the universe. This is the sense in which life is insignificant and pointless, extremely limited in time and space. We are tiny beings on a planet in an unremarkable solar system in a galaxy with hundreds of billions of solar systems - and there are hundreds of billions of galaxies. It would be hard if not impossible to write an understatement that tops this one: we are not the center or point (raison d'etre) of the universe. The cosmos is coldly indifferent to our fate. Everything is devoid of lasting consequence.
Billions of people, however, believe their lives have enduring significance. Acculturated from birth to see themselves as cosmic celebrities, special beings created by a god who loves them personally and will, after death, invite them to dwell forever and ever in a really cool place. This conviction would give anyone a strong sense of cosmic significance. Nice work or retirement, perhaps, if you can get it, that is, if true. However, there is a downside to such thinking. In the Christian court of no appeal, believers in this cosmic meaning may be found guilty of not having loved the god sufficiently, in which case eternal horrors await.
If the cosmic significance I've just described sounds preposterous, and you suspect I'm making this up (and I wouldn't fault you for that - it does sound bonkers), then check the obituaries of your local paper. Here you will find accounts of people who, despite dying, are said to have transitioned to a glorious place of eternal bliss. (Oddly, I've never seen an obituary notice that the departed is now burning in hell.) Or, be a bit more scholarly about it: read David Benetar's 2017 book, The Human Predicament: A Candid Guide to Life's Biggest Questions.
Alas, there is zero evidence and even less likelihood of heaven or hell. Thus, this kind of theological take on cosmic meaning has to be embraced on faith and more than a few grains of proverbial salt. But, then again, maybe that's what it takes to get into The Good Place.
In a terrestrial sense, of course, our lives do have meaning, do matter, enormously, not only for ourselves but to others and, in some cases, perhaps to a whole tribe, a village maybe, hell, in some rare cases, to the whole of mankind, in some way - for a while, at least. Think Paine, Lincoln, Darwin, Ingersoll, Dawkins and Harris - and the list of your own heroes, past and present.
Terrestrial meaning must be the dew and rain, seed and soil, air and light of REAL wellness - the beating heart of being well that makes the human predicament less burdensome. Terrestrial meaning might entail what Peter Singer termed a transcendent cause, one beyond the boundaries of the self. Viktor Frankl created an approach to meaning linked to mental wellbeing called logotherapy, based on the premise that we are motivated by a will to meaning, an inner pull toward animating purposes that make life worthwhile. Nietzsche's way of capturing this aspect of terrestrial meaning was to say he who has a 'why' to live can bear with almost any 'how.'