"Network is unreachable" while defining specific route

Tun1 is my VPN tunnel. I don't understand why I get "unreachable" here:

# ip route
default via 192.168.1.1 dev wlan1  proto static 
10.1.0.0/16 via 10.9.0.5 dev tun1 
10.9.0.1 via 10.9.0.5 dev tun1 
10.9.0.5 dev tun1  proto kernel  scope link  src 10.9.0.6 
192.168.1.0/24 dev wlan1  proto kernel  scope link  src 192.168.1.66  metric 9 

# ip route get 10.1.1.1
10.1.1.1 via 10.9.0.5 dev tun1  src 10.9.0.6 
    cache 

# ping -c1 10.1.1.1
PING 10.1.1.1 (10.1.1.1) 56(84) bytes of data.
64 bytes from 10.1.1.1: icmp_seq=1 ttl=63 time=40.4 ms

# ip route add 157.166.226.25/32 via 10.1.1.1
RTNETLINK answers: Network is unreachable

# ip route add 157.166.226.25/32 via 10.1.1.1 dev tun1
RTNETLINK answers: Network is unreachable