Im planning on advertising for a network security gadget I invented. You said you're "useless" in other domains. That's not good news for little old me who is g

Im planning on advertising for a network security gadget I invented. You said you're "useless" in other domains. That's not good news for little old me who is going to try and make the ads himself. I've heard about testing ads for your various demographics before you go all in on an advertising campaign. But it sounds like there is even more to it. Why do you feel like you would be useless in another domain? Surely you would do better than some geek off the street.