Think for a moment about the meaning of the word.
Literally it means: "things that happen at the same time".
But there's a little more to it than that. Things happen together all the time, but we don't call every simultaneous happening a coincidence.
Two things happening together form a coincidence when cause and effect appear to be at work, but in fact are not.
Here is an example: A boy trips and falls while running along the sidewalk. A stranger helps him back to his feet and says: "No wonder you fell. Your shoe-laces are untied." Cause and effect? No. The actual cause of the boy's falling was a discarded banana skin that he stepped on. His fall and his untied shoe-laces were coincidence.
Human beings have a powerful need for explanations of what happens in the universe. Explanations help satisfy the instinctive need for security and self-protection that we all have.
Such is the strength of our need for explanations, that sometimes we devise theories and believe in connections that contradict the evidence of our senses.
People love to attribute cause and effect, even when common sense tells us that it's just coincidence.
So what is the point I'm making here?
When two events appear related, stop and think before you conclude that they are. Be observant and consider all of the possibilities before you make a decision about what just happened.
Looking beyond what seems to be obvious is what scientists are trained to do. But it's not rocket science or brain surgery. It's just common sense!