Targetings and limits
If the campaign that you're making a forecast for has limits or targetings that reduce the amount of available inventory and explicitly affect the number of impressions, they'll be listed under the forecast.
The list contains the potential number of impressions that the campaign loses due to these limits or targetings:
If the forecast shows that the campaign may not be completed, you can simulate how disabling targetings or limits will affect the campaign. To do this, exclude a limit or targeting from the forecast by clearing the checkbox in the appropriate line and update the forecast. The line with the excluded parameter will turn gray (meaning that the parameter is not included in the forecast).
To add the limit or targeting back to the forecast, select the checkbox and update the forecast again.
Recommendations on what to do if a campaign might not be completed are given in Forecast analysis.