You were nervous. Would they like it as much as you did? Would you make the cut? Your first manuscript as a senior author tends to be a memorable experience. On one side, you have been working a long time, coming to terms with the problem, learning, building models, polishing the words [insert a few iterations here] until you submit the manuscript. It is a hopeful act.
Do you remember the feeling of the first acceptance? Your work was judged good enough to be published in that special journal, the one you like. The one were so and so, the authors you admire, published their work. Later you’ll understand that there are diminishing returns, so your tenth article will not provoke the same reaction, and your fiftieth article… you get the idea.
Do you remember your first rejection? Was it just a “desk-rejection”, wrong journal, no big deal? Or was it a “we hate the manuscript, what a turd”? This one can hurt, but there are diminishing returns too: your tenth rejection is more like “meh, what do they know?”.
Both the acceptances and rejections are of that particular piece of work. They are not about you, although some referees (typically referee No2) sometimes manage to make it feel personal. You are not a better or worse person because of the comments of a random set of referees. It is good to remember that a different sample of referees could have told you something very different about the manuscript.
I do remember the first acceptance; I barely remember the first rejection. I do look at those experiences with older eyes, thinking that in both cases I would write the manuscript very differently today.