How do I make sure my snake never escapes?

I hear that even experienced snake owners have had their snake escape its enclosure before. I’m thinking of fostering a snake, but I’ve never owned a snake before. I live in an apartment with a cat and am very paranoid about it escaping since I hear they can be escape artists.

What mistake did you make that caused your snake to escape, and how can I be 100% positive it will never happen?