Runnells explains on the Mormon Stories Podcast that he learned things about Church history and felt "betrayed."
"Mormon Stories 480: Jeremy Runnells Pt 1 - On Growing Up Mormon and the Genesis of the CES Letter," Youtube, June 21, 2014
Jeremy: It's not just being exposed to the information but the feeling of betrayal in the sense of why hasn't the Church told me this? Why haven't I learned this before? Why am I discovering this now at 30 and 31-years-old? And if I've never heard of something as crazy as Joseph Smith marrying other living men's wives...what else don't I know about?
So, that question really took me on this crazy path of research. I became absolutely obsessed with Joseph Smith, Church history and the origins of the Church over the next year or two.
John: What were your main sources of study or learning?
Jeremy: It was Rough Stone Rolling. I've looked at FAIR. I've looked at MormonThink. I relied a lot on FAIR because they were in the front trenches of this. I mean, Richard Bushman, it was more of a scholarly, it wasn't really in the trenches in terms of apologetics. So, FAIR just made things worse in the sense that I read about this, then I learn something new and then that leads to something else and it just created this thing just kept going on. I was learning this and this and that and this.
I don't know. I mentioned in my Debunking FAIR's Debunking that I really looked to FAIR as a lifeline during my faith crisis and it ended up being weights that drowned whatever left I had of a testimony.
So, yeah...that year, it was a struggle.
Timestamp: 33:23 - 35:19