Nothing is wrong with your plant - that's a very handsome looking Brugmansia you have there! There is a bit of insect damage to the leaves but nothing critical. And it is the nature of insects to feed on plants - it's only us humans that insist on perfection. Nature just lives with imperfection :-)

If you want to limit the insect damage, I'd suggest going out at dusk and closely examining the foliage, especially the underside of the leaves and on the stems. It's quite likely there is some sort of larval insect present munching away and once located, they can be removed manually.

Although that amount of damage is considered minor, you probably would like a few less holes. To help slow the responsible critters, look underneath the leaves. When I lived in California, small caterpillars would eat from the undersides of the leaves where they were hidden from view.

Caterpillars are often those of butterflies. This search would be a good place to begin an investigation, to see if Brugmansia is a host plant of some kind of butterfly. If one is planting butterfly host plants, losing some leaves seems like a good trade to me:

https://www.google.com/?gws_rd=ssl#q=brugmansia+butterfly+host+plant

If it's something less desirable, throw them out in the grass to be a meal for birds or some critter.