I have made numerous smachot Baruch Hashem and together with the joy I felt there was also an element of hurt. Namely, by all of the people who were invited but didn't show up or who showed up, said their perfunctory mazel tov and quickly exited. [BTW, I don't attend funerals because I figure - he's not coming to mine so why should I go to his?? I made that up. I have gone to many funerals. It isn't much fun unless it is a terrorist but a big mitzva and stark reminder where we are all going]. I understand that there are a lot of smachot and many, many different things to attend to in life but still there is something to the wonderful feeling of people who are truly partners in your simcha. Not only that, but when a person spends so much valuable time and precious money [often borrowed] on making a simcha and then he sees that people are not into it and even see it as a burden [already making their escape plans minutes after entering - I know because I do it myself] it is not the best feeling. I understand and understood that it has nothing to do with me, I shouldn't take it personally and that people are just busy-busy-busy but still...... It was especially bothersome to see how much effort I made to attend someone elses simcha but when it was my time he didn't make any effort at all to attend. Of course, one can be מלמד זכות and one should be מלמד זכות - but there is a valuable lesson to be learned.
One avoda is to feel the pain of others. A much more challenging avoda is feeling the simcha of others. Showing up, staying for a while and being fully engaged. When I attend a wedding and see a man dancing the night away and then attend another wedding and the same man is either eating, talking or texting the entire time, I wonder what changed. The answer is that one wedding was that of a relative or close friend while another was of someone more distant. I understand that human nature is to be more involved in a simcha that a person feels closer to but we are supposed to transcend our innate natures. What is the Baal Simcha guilty that you don't feel so close to him or care so much that his son is having a Bar Mitzva or a wedding??
I recently went to a Bris where there was a nice crowd for the actual Bris part but probably three quarters of the people left before the seuda. The tables were filled by [among others] poor people who frequent simcha halls for the free food. But very, very few friends [relatively speaking].
So we can't all attend every simcha around. But we can try to attend as many as we can and when we are there to try to make the Baalei Simcha feel that we are with them in their time of joy.
There is little joy in celebrating alone.