wdt_reset(); watchdog not working

My simply Code is
#include <avr/wdt.h>

void setup() {



void loop() {

1.Why did arduino self reset? (My result is only Start)
2.Why watchdog did not reset?

Thank you.

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1.Why did arduino self reset? (My result is only Start)

That’s what happens when the watchdog times out.

2.Why watchdog did not reset?

It did, then you had a 6 second delay that was longer than the 4 second watchdog timeout you set.