In chapter one of Germinal by Emile Zola, we meet the protagonist of the story. For a time we do not know his name, but eventually we learn that he is Etienne Lantier, an out-of-work Frenchman who is looking for his next place to land, so to speak. He is an educated man, but that does him no good here in the barren land between Marchiennes and Montsou on this bitterly cold early morning in March.
Your question refers to the man's hands, which have been cut by the stinging winds. It is true that he could put them in his pockets to avoid this problem, and he does. There is something else to consider, however, before we label this as an unrealistic detail in this novel which is acclaimed as being realistic. Here is the passage where we read about his hands:
The man had set out from Marchiennes about two o'clock. He walked with long strides, shivering beneath his worn cotton jacket and corduroy breeches. A small parcel tied in a check handkerchief troubled him much, and he pressed it against his side, sometimes with one elbow, sometimes with the other, so that he could slip to the bottom of his pockets both the benumbed hands that bled beneath the lashes of the wind.
Notice that the man is carrying a package. Without that, he would certainly be able to keep his hands in his pockets at all times if he wished to do so. Instead he has to try to hold the package against his side with his elbow, and we know that is an awkward thing to do, at best. Add to that the cold and the wind and the ten miles of walking (the distance between the two towns), and it is likely that he had to keep at least one hand out of his pocket during some of the walk, probably alternating them as needed.
I agree that this detail is worth the question; however, the details support the reality, at least to some degree. When I read the novel in its entirety, I am struck by the gritty details on every page and this one does not bother me. Movies all have these kinds of things, minor discrepancies such as a character holding something in a different hand or a little different camera angle, and we suspend our disbelief and appreciate the story. We overlook them for the sake of the bigger picture, which is probably what you will have to do here.
The bleeding hands are just a detail, but perhaps this is a detail which can create some doubt as to the realism of the story.