I was just thinking about this this morning. What the heck is with the "-er" suffix?

"I'm a witcher."

"What does a witcher do?"

"I ~~create~~ ~~watch~~ ~~catch~~ ~~breed~~ ~~f***~~ hunt witches."

"I'm a birder."

"What does a birder do?"

"I ~~create~~ ~~catch~~ ~~hunt~~ ~~breed~~ ~~f***~~ watch birds."

"Actually I think several of those could apply..."

I think the confusing-ass formula is this:

A [word1]er is a [word2]er of [word1]s.