Have you noticed that some people naturally go with the flow, while others desperately cling to the status quo, as if their lives depended on things staying the same? The latter, of course, is a losing battle, because change is the natural order of things here on planet earth. Like the seasons of the year, all the stuff of 3-D life has a beginning, a middle, and an end. Time passes, our children grow up and leave us, dream jobs (and nightmare jobs) end, old pets die and new ones appear.
Some people or groups have (woven into their cultural or constitutional fabric) a very comfortable and reality-based view of life. For instance, in India, the roles of creation and destruction are weighted equally. Kali, the Goddess of time, change, and destruction, is respected and revered. Birth and death are simply two sides of the same coin.
Similarly, Buddhist philosophy embraces the concept of impermanence, not only because accepting what is leads to peace, but because they place a premium on living in the present moment, instead of dwelling on the past or projecting into the future. If you live for the richness of the real here-and-now moment, you take things as they come, and are less likely to compare and rate your experiences as "better" or "worse."
Here in the United States, we are culturally more likely to judge our experiences and conditions, and reject the changes we consider to be "negative." Birth is good, death is bad. Losing weight is good, gaining weight is bad. Staying young is good, aging is bad. We each have our own criteria for what we like and what we don't, but chances are we have attitudes and beliefs about how our lives should be, which set us up for a fall when these things change or don't pan out. (We're a little spoiled this way.)
I remember once going to a memorial service for an elderly relative who had passed away. I had two babies at the time, and asked if it was okay to bring them along. My cousin said, "Absolutely! I think it's very important for people to be reminded that along with death comes new life. Sometimes at funerals, we forget that."
And so I invite you to remember that change is inevitable. This means that not only will our happy moments pass by, but so will our difficult ones. Each moments is an opportunity to enjoy what we have and who we are, knowing that while the things of the world are temporary, the energy we carry (like our love for others) is permanent. Energy doesn't die; it only changes form.