For a significant chunk of my adult life I was a fundamentalist, charismatic Christian--part of the Vineyard churches. Some good came out of it (particularly meeting my wife there), but I also have many regrets about it. The most important lesson I've taken away from that time period is that just because someone claims with absolute certainty that something is true, it doesn't mean it's true.

Very few of the leaders--pastors and teachers and "prophets"--had graduated from college, much less had any formal or systematic theological training. Some were, I realize now, very needy people--seeking to be looked up to but also unwilling or unable to put in the real work necessary to be bona fide authoritative figures. Most were well-meaning but ignorant; confident that they had the answers (and that those answers shouldn't be questioned too deeply). They taught an unscrutinized mishmash of (often contradictory) doctrines. They claimed to speak God's will, making pronouncements about people and giving direction to people's lives. It's horrifying, now that I look back on it, the authority that some of them claimed for themselves. Some of them are still at it