Lack of self-confidence can be difficult to explain, but common sense suggests that stuttering is among the causes, judging from how often the two things go together
A. The stated “cause” might really be the effect, and the stated “effect” might really be the cause B. This may well just be coincidence C. The “cause” and “effect” might actually both be the effects of the third thing D.
Legitimate cause and effect It’s odd. I’ve seen a huge number of snails this year, and the roses have mildew. Don’t know which caused which, but one of them obviously cause the other