Lacking any other way to navigate at this point, Childermass isn't as inclined to argue with Lambert (as one-sided as it would be) when he drops his other hand on his shoulder. If the witcher is willing to lead, he's just going to have to trust him. He turns away from the lake when Lambert does, no need for the extra push.

"Just try not to walk me right into a lamppost," he says in a fairly resigned manner.