Survey - sort of; regarding en-/decryption

Hi there!

After trying around, reading a lot here and asking sometimes (mostly without getting answers or hints) … just a plain question if my feeling could be right;
On whatever reason decryption fails (and regardless it seems to have been an idiotic idea to use the feature e2e of nc or not) … is it true, that once any battle was lost against encrypt/decrypt it ends up in all files lost forever?

Thats my feeling after months of try&error - sad to say so but true!

So - if my feeling is right … what method should be more failsafe to protect files?
Or is there simply no way inside nc to suppress any unwanted third party filereading?