One might assume that missing is the act of failing to connect with a goal, or failing to coincide with a particular event in spacetime, or losing out on an outcome to which one has been working.

You missed the bus, you missed out on meeting up, you missed the party, you missed your chance.

Another way to consider missing, however, is to consider that the opportunities which one would have closed down by connecting with one's assumed plan are still latent. In missing the opportunity to have a romantic relationship with that person, you still have an opportunity to have one with those people - some of whom you may have yet to meet. In missing being hired for this job, you may (or may not) have opened yourself up to the possibility of many others.

If the onrushing universe of experience must be whittled down to a manageable level by our ability to use our past experence to model the present and thence project our assumptions into the future, then everything we feel we have missed in the present must also be considered to leave a vast tract of potential experience open to us in the future.

So, chin up.