Since Google doesn't tell you why they're showing this warning to you, and only tell you to follow standard security guidelines ("don't get phished"), I suspect

Since Google doesn't tell you why they're showing this warning to you, and only tell you to follow standard security guidelines ("don't get phished"), I suspect people will quickly be trained to ignore this message. My girlfriend received the warning message today. She has already activated 2-factor auth, so I'm really not sure what she's supposed to do with this information.