People can feel that life is meaningless because they do not matter to the “big picture.” I remember a debate about this in first year philosophy: your life is meaningless, because what matters to you will not matter to people a thousand years from now. An objection was immediately offered by the lecturer: if what matters to you is unimportant to them because of that thousand years, then what is important to them is unimportant to you - so it shouldn't matter to you that you don't matter to them, for the logic cuts both ways. That is a good point, but a logical argument like this does not strike deeply enough. There are more important things to say.
The more important issue here involves perspective and character. The opposite of those two is one thing: arrogance. The universal struggle of life - insofar as we actually do struggle with it – is against our "fat, relentless ego" as the philosopher Iris Murdoch used to put it. When a person says that either I must matter in some big way or I do not matter at all, they are not expressing some deep insight, nor giving voice to some profound existential problem. Rather they are giving voice to their ego.
Why does every great, ancient philosophy of life, from both the East and the West, speak loudly of the problem of the ego, about the way it poisons our lives, while modern psychology often ignores the issue, pretending that our problems are technical ones? This applies also in modern philosophy, which treats our problems as fundamentally intellectual in nature. No wonder we become so passive, and look to experts and pills to do something for us. We miss the main point. This problem is in our control. As I say, it is one of the central struggles of human life.
What do we know about happiness? Well, modern science has much to say. From the research we know that certain personal qualities or strengths improve it, and that among the best of these is both gratitude and kindness. If you practice both of them until they are a part of your way of being then, all things being equal, you will become happier. This is age-old wisdom, but in 2017 it also has solid empirical evidence. And these are the sorts of qualities which are the opposite of egotism, as the Buddha, as Socrates, as Christ, taught us so long ago.
Forget about mattering to the big picture. That is not where your life has its fundamental meaning. Sure, you may have some butterfly effect on the greater good, but like the vast majority of us the good that you do in your life will be toward individuals around you. And the relationship you have with life – living in a spirit of honesty, curiosity, love of the world – may never be recognised widely, but nonetheless it matters greatly for the meaning of your life. Living a life of gratitude and kindness will make your life meaningful no matter how invisible you are to the world. It is in the small picture - the daily action, the invisible - that the richness will be found.
It is not necessarily arrogant to want to change the world. But it is arrogance to think that doing something great is the necessary or primary way of having meaning. It is arrogant to get depressed because you are not creating meaning at that level. It is wrong to lose your sense of meaning because you do not matter to the big picture. An ancient saying tells us that wisdom begins with humility. So does gratitude, so does kindness - and so too, therefore, does genuine meaning. If you look at the big picture and decide your life has no meaning because it does not affect things at that level, then you are looking in the wrong place.