Running ads in the digital world is far from perfect. It is much more reliable a billboard in the highway. Of course, you miss all the perks of measuring how many people saw your ad and ended up as a customer.
When you are running ads on multiple publishers, on various devices, driving people to different landing pages, anything can happen. A spike in traffic (due to bots) could be as bad as not traffic at all (due to Unbounce being down.)
Make sure to have alerts in place for any possible anomaly that could affect the performance of your campaigns. For example, you can use Pingdom to alert you if your domain is down, or subscribe to Unbounce’s status page to know about any significant outage.
Anything can fail while you are running an online campaign, and the sooner you can take action, the less money you will be wasting.