I think this is explained pretty well in other comments.
It blew, and took some getting used to. I didn't finish my mission. I was depressed, couldn't sleep, had no appetite and my medication only made it worse. On top of that, I was homesick. I had a girlfriend that I wanted to marry back home. First zone conference in Italy I met with my mission president and asked to go home for the depression, and he told me to stick it out, promising it would get better. I was having none of that manipulative bullshit, so I confessed to pre-marital sex (I hadn't confessed before my mission.) The next day I get a call telling me to get my stuff and hop on a train immediately; I was going home. Morning after, I was on a plane.
I was a "fence sitter" a lot of my life, and decided I was done with that. I was going to find out whether the church was true or not, and follow wherever that answer led. I read a lot of "anti" material, hoping to strengthen my testimony, and I was able to explain a lot of the problems away. The breaking moment was the Book of Abraham facsimile. Joseph pasted not only the incorrect text into the gaps, but also the incorrect writing style. Like cursive and standard. He also got the name of every single Egyptian god wrong. Either I had to believe Joseph, or the Egyptians and Egyptologists. He was clearly being deceitful, and there was no way around that. I had my answer; the house of cards fell.
I was an agnostic Mormon upon taking a philosophy class and falling in love with religious philosophy. Upon leaving Mormonism, I became an agnostic theist, clinging to a god's (and afterlife's) existence out of my fear of death. When I was able to confront my own fear, and studied religious history and mythology, I ended up where I am now: agnostic atheism.