The operator is just syntax sugar for something roughly this let foo = foo()?; // Expanded let foo = match foo() { Ok(v) => v, Err(e)

The operator is just syntax sugar for something roughly this let foo = foo()?; // Expanded let foo = match foo() { Ok(v) => v, Err(e) => return Err(From::from(e)) }; If you're using your own error type then you can impl From/Into yourself to capture additional context from the source error (or a stacktrace) in addition to using map_err() as others have suggested