"Happen to + V" Explanation

“I happened to see him yesterday at the club.” “I happen to know the recipe.”

Yes, if something “happens to” occur, then it doesn’t occur by necessity, but simply by chance, or “happenstance”. Similar is the construction: “it just so happened that X occurred.”

It describes something that might not be expected so has a small element of luck or surprise involved. You may also hear 'as it happens' as in "I went to Brighton yesterday for a day out." "Oh really? As it happens, I grew up there." OR "Oh really? I happened to grow up there."

To make it a bit clearer, the "to" here is kind of part of whatever verb follows this phrase. And "happen" is like "to be" but for verbs, i guess. This phrase is really just an extra detail to make clear that you aren't stating a cause for the event. This isn't needed at all in most cases, so don't worry about applying it, just know what it means when you hear it. Extra: Really the only time this would be needed is when you are implying a cause for an event, but stating that you aren't. For example in this dialogue here: Person 1: "I was thinking about asking Sarah out." Person 2: "You know she has a boyfriend, right?" Person 1: "Yeah, but what if he happened to die of radiation poisoning?" Here the "happened to" states that there is no intention of how the boyfriend might die of radiation poisoning, but it is implied that Person 1 is going to put Uranium in the boyfriend's lunch.

It's often used to describe something that isn't essential, but if you've got it you can use it. For example, if I'm making a cheese omelette and I happen to have some mushrooms, I may as well throw them in. If I see a funny sign and I happen to have my phone, I could take a photo of it.