Grateful people experience the world fundamentally differently compared to ungrateful people. Obviously, most people are not 100% committed in either direction, but there are certain principles of thankfulness, and if we convert ourselves to them we will be much more likely to feel gratitude on a daily basis.
And in nothing doth man offend God, or against none is his wrath kindled, save those who confess not his hand in all things, and obey not his commandments. - D&C 59:21We depend on God for everything and do next to nothing in our lives completely independently. We should all recognize that we cannot control the world. We can plant crops but we cannot make it rain; we can graduate college but we cannot force job openings; we are constantly at the mercy of the unknown and uncontrollable. There is One to whom nothing is unknown or uncontrollable, and we should recognize His influence and guiding hand in our lives. When we accept that our successes are not ours alone, it becomes much easier to be grateful for them.
Another key difference is pride. We can consider the example of working to advance a career: one works for a few years and achieves a promotion. A prideful man may see the promotion was long overdue, minimizing any gratitude and joy for the improvement. A humble man will recognize that many things factor into a promotion: the company must be doing fairly well, have the money to increase payroll, efforts must be recognized, the boss must appreciate him, etc. Many of these things cannot be controlled and should be attributed to Grace. Humility has a myriad of benefits of which increased gratitude is one.
True gratitude makes life rich; the lack thereof can make even the rich poor. I testify that this is true and that I have experienced it in my own life.