I learned to use cisco packet tracer and found something confusing. So i tried building this simple lan setup :

PC 192.168.1.10 ---> switch ---->  router A (192.168.1.1 / 10.0.0.5) ------> router B (10.0.0.4)

The router A has LAN IP 192.168.1.1 and WAN IP 10.0.05

In my setup :

PC IP is 192.168.1.10/24 and set gateway to 192.168.1.1

i can ping from PC to 192.168.1.1 (LAN IP of router A) 

i can ping from PC to  10.0.0.5 (WAN IP or router A)

The problem is : if i disconnect router B from router A

i no longer can ping to 10.0.0.5 . Why is it ? why it depends on the connection of router B while that IP (10.0.0.5) has nothing to do with router B

If i reconnect again router A and B, then i now can ping from PC to 10.0.05

How does it actually works ?

Thanks