This unit loses 5 HP at the end of your turn if it did not successfully attack. Every time a friendly champion within 3 spaces successfully attacks, this unit gains 1 AP.
Impatient is a great example of an ability with moderate strength and a moderate drawback. 5 HP loss is significant (and a larger loss than that from Semi-Aquatic) but if the champion keeps making successful attacks, this won't trigger. What's more, this is useful for getting two attacks in each turn, when the champion might usually only get one.