Latin helps here...a little bit. The root of both words is the same: the verb facio, facere, feci, factum, which means "to do, make." Ad- as a prefix means, generally, "to" or "toward," so afficere means, basically, "to do to" hence "to influence," and the noun affectus means "the result of things done to one," like emotions (affection is related). The prefix e- means "out of/away from," but it's a longer walk to get to the meaning "to accomplish, cause" for the verb efficere, though English "efficient" in the sense of "working things out" shows the idea. The passive sense of effectus, that is, results, accomplishments, effects, follows more naturally as "things worked out." But I agree that they are confusing. I nearly always stop and think about these every time I use them, whether noun or verb.