Honestly, it can be a multitude of factors.
It is a coincidence.
It is a form of the universe sending you signs so you could learn something.
It is your own mind creating circumstances unintentionally.
All of these (and probably several others) can cause the results you've seen. If you pay enough attention to the universe, you will find it constantly is sending signs specifically to you, but also to many other people. Unless you are open to finding a sign, or it is particular to your situation, you will pass it by without seeing or knowing it. For instance, a lady smiles at you at the supermarket, and you are too busy or too out of it to notice it, and as a result, you miss a sign that says good things will come into your life. Other times, you will see signs that are meant for another, and unless you know this person well and/or are speaking to them at the time, you will completely miss it.
At the same time, you can create circumstances within your own mind unintentionally. In these moments of unintentional causes, your mind picks up on all of the information coming in, the sad songs, etc, and it causes an outcome aligned with what it's focused on. So if your mind is focused upon the negative, then you will get negative in your life. It can be as simple or as complex as that.
Honestly, you should follow your intuition and experience in cases of whether things are a coincidence or not, and if you do not have any experience in it, then you are best examining the situation and determining from there whether or not to consider it coincidence or something else.