systemd can't start a dæmon and doesn't give any error either

[Weiwu Zhang <a@colourful.land>]

To show this dæmon itself is properly configured and runs fine on Debian 9.5:

# su bitcoin
$ cd
$ /usr/local/bin/bitcoind -daemon
Bitcoin server starting
$ pgrep bitcoind
3946

However, it won't start if converted to a systemd service:

# cat /etc/systemd/system/bitcoin.service
[Unit]
Description=bitcoind
After=syslog.target

[Service]
User=bitcoin
ExecStart=/usr/local/bin/bitcoind -daemon

[Install]
WantedBy=multi-user.target

# systemctl enable bitcoin.service
# systemctl start bitcoin.service
# pgrep bitcoind || echo "not working"
not working

There were no error messages:

# journalctl -u bitcoin.service
-- Logs begin at Mon 2018-10-08 03:53:55 BST, end at Mon 2018-10-08 11:14:47 BST
Oct 08 11:08:54 lightning systemd[1]: Started bitcoind.

There weren't error messages even if I add these in
/etc/systemd/system/bitcoin.service

StandardOutput=syslog+console
StandardError=syslog+console

I assume this question is best addressed in Debian list because
normally bitcoind would through some error message. No error message
could mean the whole command isn't executed.

Thanks!