Have you ever heard of the concept of mental priming? Ideas you encounter early in the day will impact your mindset later in the day, even if they're really subtle.
Tony Robbins did a great example of this on the Tim Ferriss podcast - I think this online version is similar https://www.tonyrobbins.com/priming-exercise/
The underlying study I know about is when they tested a random encounter on the street, passers-by were more likely to remember a stranger fondly if he handed them WARM coffee. They were likely to dislike the stranger if he handed them COLD coffee. It's a weird phenomenon.
By fixating on the number "777", you primed yourself up for a great day or more. The lucky number manifests itself in real life!
Huh, thanks I'll look more into it, I have only been experiencing synchronicity noticeably for the last few months, but I'm enjoying it.