SoftwareSerial wireing software-TX to hardware-RX not working

I guess there something fundamental that I do not understand.

I try do some simple test to check whether my softwareSerial is working.

I did wire the software TX (pin 9) to the hardware RX (pin 0) writing every second a message to the software serial. I would expect that this message shows up in the Serial Monitor (configured at 9600). However, this fails, I only get to see the message that is sent to the hardware serial during setup().

For the wireing I tried a 1K resistor as well as connecting the two pins directly. I tried this on an arduino uno as well as on a nano. The nano has an RX-led which blinks once a second. So I know something is arriving there.

What do I not understand?

#include <SoftwareSerial.h>
SoftwareSerial xbSerial(8, 9); // RX, TX

void setup() {
  xbSerial.begin(9600);
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  Serial.println("Goodnight moon!");
}

void loop() {
  // the xbSerial TX is wired to the hardware RX, expecting 
  // to see this message once a second on the serial monitor
  xbSerial.println("ldkajfdsalkjfdslkfjdslkfjdsalökfjdslkfjdsalkfsdlkfj");
  delay(1000);
}

Serial.println( ) causes the output to appear in Serial Monitor

xbSerial.println( ) causes the output to go into hardware serial RX
nothing is going to be printed to the Serial Monitor unless you write code for it.