memory - How is Deleted Data Recoverable Even When Overwritten?

Would this make a file unrecoverable (Windows OS)?

1. Delete the file (i.e. send it to the recycling bin).


2. Empty the recycling bin (i.e. remove the reference to where the data is stored in memory).


3. Overwrite the memory with different data (assume you knew the blocks of memory used, and forced those to be used with new data).

I've read that only once overwritten several times the data is truly unrecoverable. Is that true? How could the data be recovered if the memory where it was store has something else stored in it?