Pipeable/lettable operators are functions that are passed an observable and return an observable, so there’s no source observable for the
retry operator to be connected to.
The source observable will be passed into the function returned by the
retry operator when the operator is applied to the source observable using
const composed = source.pipe(retry(3, 1000));
source will be passed to the function returned by the call to
retry and that function will return the observable assigned to