Koheles teaches that this world is הבל הבלים. The word הבל means [among other things] hot air. Everything in life eventually just dissipates - like hot air.
Think of all of the friendships you have had in your life, from nursery and on. School, shul, summer camp, neighborhood etc. etc. How many of those people are still your friends? VERY few. Like הבל. Gone into thin air [if the air was thick it wouldn't help].
You raise children - they grow up and move out. Gone. It is never the same. Just the pleasure of holding a newborn baby is so fleeting because he is a newborn for such a short period of time.
You are enjoying a few days in a nice hotel. It's AWESOME. But then it is checkout time and the experience is over - FOREVER. You can go to the same hotel again next year [if you have the mean$] but it won't be the same. It is never the same.
You are eating a meal in a fancy restaurant with someone you love. You are savoring every second. Then the meal is over, you pay the bill - and that's IT. FINISHED. FINITO.
You have a job. You like the job [together with parts of the job you don't like]. But then the ax is grinded and you are told that you are unwanted and unnecessary. Bye-bye. Sad - but so it goes for so many of us.
Parents die. Relatives die. Friends die. Every newborn baby is destined to die. The biggest and most shocking news is that YOU are going to die. As I write my body is slowly but surely aging. I am 20 years into the process of old age [it starts at 26]. We don't go towards life but rather steadily towards death.
Sweet friends - my challenge to you is to think about how we can stare reality right in the face and still be FILLED with simcha [after all - we read Koheles at זמן שמחתינו]. Because we CAN and we MUST.