Which factor is difficult to assess in a cost–benefit analysis?

i dont know about basic economy but i think is benefit and if people knows that if there is better alternative; cause people only watch for the best benchmark or something like that, also how many gonna last the product; for examples most of the people want an iphone or a samsung because is most knowedge trademarcks(except iphone has a large), or for example, you prefer to buy aloe vera or a drink based on aloe vera, obviously you rate the natural one because it has all their properties, but you have to prepare it, you obtain more for less, instead, drinks based on it has little cuts of it, are more expensive and has less nutritional facts. you obtain less for more

well thats it, sorry for write the holy bible but idk about economy so perhaps is not the answer that you search