I applied to speak at WordCamp Miami in 2015 and again in 2016.
Last year, I was lucky and got accepted.
This year, I was lucky and didn’t get accepted.
Why was I lucky? Because I got this email from David, the organizer: 
I’ve never had a reply like that from a conference before.
Not only does David organize the biggest regional WordCamp in the US (and perhaps further afield), but he takes the extra time to write a personal note to over 160 speakers who weren’t accepted.
Maybe those two things are related.
Going forward, I’ve printed out David’s reply and will use it as a reminder of how to deal with our own customers.