Someone knows (of) two people who died recently. They were never close to her – she’s basically only heard of them through other people – and they weren’t famous. The two people didn’t know each other and didn’t have anything unusually in common. But they’re two deaths that she’s had conversations about so she knows another one is coming. They always come in threes.
…except they don’t. Hundreds of thousands of people die every day. Statistically about 25 people in this city are going to die every day, and depending on variables in your networks, family tree, and social circles there are not impossible odds that you will know three of the 175 that adds up to in a week.
And celebrity deaths – they’re only selectively noticed based on who’s death is widely reported on and what entertainment you’ve consumed over the years. On Wikipedia’s Recent Deaths page there are well over three notable people who die every day.
So consider the math before buying into superstition. Consider your selective attention bias. And consider that you’re just idly trying to leak hot air because you have nothing of more substantiated meaning to say.