Why you keep seeing 333
In brief
You may keep seeing 333 because of how attention works: once a pattern matters to you, your mind flags every instance and forgets the misses. That doesn’t make the moment meaningless. What you do with it is what gives it meaning.
The frequency illusion
Once something catches your attention, you start noticing it everywhere. Linguist Arnold Zwicky named this the frequency illusion in 2005; it is also known as the Baader–Meinhof phenomenon. Clocks, receipts, licence plates and page numbers show you hundreds of numbers a day, so 333 has plenty of chances to appear.
Seeing patterns
The tendency to see meaningful connections in unrelated things is called apophenia, a term coined by psychiatrist Klaus Conrad. It helps us learn, and it also makes coincidences feel like messages.
Synchronicity
The psychiatrist Carl Jung used the word synchronicity for coincidences that feel meaningful to the person who experiences them. You don’t have to believe anything supernatural to find the idea useful.
So what should I do with 333?
Use it as a trigger. When it appears, make or say one small thing you have been holding back. That way, 333 helps you either way.