You may be configuring a Realtek 8188EUS wireless adapter on Gentoo Linux, and everything looks fine except for wpa_supplicant. Thanks to The Linux Rain, here is the right command to connect to the network. But if you want the wireless network to come up at boot, just add a few words to the file /etc/init.d/wpa_supplicant, and make sure /etc/init.d/wicd starts well before /etc/init.d/wpa_supplicant. File content before editing (line 8):

command_args="$wpa_supplicant_args -B -c$wpa_supplicant_conf $wpa_supplicant_if"

After edit:

command_args="$wpa_supplicant_args -B -Dwext -c$wpa_supplicant_conf $wpa_supplicant_if"

Make sure "wicd" service started long before "wpa_supplicant"

# rc-update add wicd default

mv /etc/runlevel/default/wicd /etc/runlevel/default/Awicd

rc-update add wpa_supplicant default

Gentoo linux 4.12.5 kernel configuration for 8188EU USB wireless adapter

Device Drivers ---> [] Network device support ---> USB Network Adapters ---> [] Wireless LAN ---> [*] Staging drivers --->
RealTek RTL8712U (RTL8192SU) Wireless LAN NIC driver Realtek RTL8188EU Wireless LAN NIC driver