you can google what serendipity really means...
sometimes people want it really happens one time
that moment when you think Lucy will be the one who will be called by teacher, and there she was. Being called. that might be a coincidence.
when the countdown of the traffic light was broken, and you didn't know when the green light would be on, but you did count from the time you stop, 10... 9... 8... 7... 6... 5... 4... 3... 2... 1..., and it's on. that might be a probability.
when you met someone, the one who make your tummy full of butterflies, in an unexpected time and place. that might be serendipity.
that serendipity that you'd been waiting for.
the wish to hit on that person accidentally that made your eyes widen looking for that familiar gaze.