-Home field advantage isn't too straight forward. Except during a Derby or other Big International match, HFA doesn't let the Relegation Threat beat the Top Teams.
-Form matters.
-Look at the schedule ahead. A big favorite may not be a good choice if a bigger game (CL, EL, Cup) is upcoming in the next 3-4 days.
-Betting on favorites in a Cup game is a suckers bet. It isn't March Madness, the #16 seed has and will knock off a #1 seed.
-Shit Just Happens. This is just as often the last minute winner for your bet as it is against your bet.