You certainly can’t judge an ad a failure if it only has 10 clicks. That is, unless you’re certain it should be converting above 10% conversion rate (CR). Some PPC managers wait for 100 clicks in each ad and keyword before evaluating them. You can go smaller if the CR warrants it.

For example, if your average CR is 5%, you’d expect to see a conversion after 20 clicks. If you have 40 clicks and no conversions, you’re looking at less than a 2.5% CR. You might pause that ad or keyword then, if you’re being aggressive. But generally speaking, the more data you have, the more confident you can be that it’s representative enough to predict future behavior.

The main thing to ask yourself is, “based on how much data I have for this, how certain am I that the data will look the same over the next 3 months?”