An ad may make me aware of a product of which I had not previously been but it's not going to induce me to buy something in which I had no previous interest.
If I'm thinking of Widget Class X Brand A, an ad might make me aware of Brand B and I may eventually purchase the Brand B but I was going to purchase Widget Class X anyway.
If I had no interest in Widget Class Z, it doesn't matter how many ads I see for it, I'm still not going to buy it.
An ad may make me aware of a product of which I had not previously been but it's not going to induce me to buy something in which I had no previous interest.
If I'm thinking of Widget Class X Brand A, an ad might make me aware of Brand B and I may eventually purchase the Brand B but I was going to purchase Widget Class X anyway.
If I had no interest in Widget Class Z, it doesn't matter how many ads I see for it, I'm still not going to buy it.