It’s not uncommon to have a conversation about something and then immediately see an advertisement pop up for it — often on Facebook (FB). Sometimes people dismiss it as mere coincidence, but frequently people suspect the social media site is spying on you.

Addressing the 2017 Web Summit conference in Lisbon, Portugal, Stan Chudnovsky, vice president of Product for Facebook Messenger, addressed these “coincidences.”

“I will be happy to shoot it down one more time,” said Chudnovsky. “No, we are not using anyone’s microphone to do any of that. We’re also not using the context of your conversations in order to target ads. None of that is happening.”

Chudnovsky said it’s easy to explain, mathematically, and that it’s not at all unusual.

“The way it’s happening is just by the virtue of people spending a lot of time on Facebook and on Messenger,” he said. Somewhere in the interactions through the Facebook Newsfeed or other behavior, the platform may learn that you have an interest in bananas and serve you an ad. To make a coincidence, all that needs to happen is that the user has a conversation about bananas offline.

“Statistically, if you look through the math and you actually compute that — and there are a bunch of studies out there — at some point it’s very likely to happen given the amount of content you’re talking about with your friends, and given the amount of time you spend on Newsfeed,” said Chudnovsky. “At some point, these two sets will intersect.”

When they do, Chudnovsky said, most people will attribute that not to a coincidence — which is more common than most people think — and instead attribute it to a simpler explanation: Facebook is spying.

“The human bias is that ‘let’s just jump to the simplest possible explanation’,” he said. “Not everyone has a math background.”

Ethan Wolff-Mann is a writer at Yahoo Finance. Follow him on Twitter @ewolffmann. Confidential tip line: emann[at]oath[.com].

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