You’ll observe how many times people stumble in serious things, not because of having wrong character traits or wrong intentions, but because they never learned. However, the blame for not learning is a very serious blame. 

Even though what they did was nothing, it was ignorance—the fact that they’re ignorant is [cause for] the biggest blame. (Mesilas Yesharim 16) ~ R’ Avigdor Miller zt”l