My father gave me a queen excluder for the first time. He installed it for me. 2 or 3 weeks later, he arrives to help me extract for the first time.
The excluder has a deep and a shallow below it and a medium above it.
The medium has brood. The shallow doesn't. The queen was on the wrong side of the excluder! And the medium was honey bound so there wasn't much brood.
Now I've had a big drop in my population. A second medium was 1/3 covered with bees. But now it has probably just three hundred bees in it.
Big time disaster. I've set back the population of my hive big-time.
Newbies, learn from me, always known where your queen is when you put on the excluder. She just might be where you think she isn't.