Causation and remoteness is a really hard one to get your head around, so this answer might help.
There are two versions. One is for explanation only, and the other is for application only. I will post both.
Explanation only.
Factual Causation is established by Barnett v Chelsea and Kensington Hospital. But for the doctor refusing to treat the patient, they would have died anyway. The doctor is not the factual cause. This concept is also explored in Chester v Afshar ... But for the doctor warning the patient of the risks, they may have died anyway if they had chosen to continue with the procedure. However, the liability comes from the doctor not warning them.
The Wagon Mound Case 1961. If harm is not foreseeable, it is considered 'too remote' from the breach and thus unclaimable. The damage by oil was foreseeable, but the subsequent fire was too remote. Hughes v The Lord Advocate showed as the type of harm of burns was foreseeable, it did not matter that it happened in an unforeseeable way like the explosion. Bradford v Robinson Rentals showed it is not necessary to foresee the full extent of the harm of frostbite.
Smith v Leech Brain illustrates the thin skull rule. The defendant must take their victim as they find them, in this case with pre-cancerous cells in his lip.
Application only
Factual Causation is established by Barnett v Chelsea and Kensington Hospital. But for the doctor refusing to treat the patient, they would have died anyway. The doctor is not the factual cause.
IF THERE ARE MULTIPLE CAUSES - McGhee v NCB established test of 'Has this breach materially increased the risk of harm?' use if relevant
Fairchild v Glenhaven Funeral Services. all defendants can be fully liable even if the specific cause cannot be identified.
Barker v Corus Liability can be apportioned between defendants.
If there are any novus actus interveniens (intervening acts) you can pick the relevant ones to a scenario
Nature - Carslogie v Royal Norwegian Government
3rd party - Knightley v Johns
Claimants own actions - McKew v Holland.
The Wagon Mound Case 1961. If harm is not foreseeable, it is considered 'too remote' from the breach and thus unclaimable. The damage by oil was foreseeable, but the subsequent fire was too remote. Hughes v The Lord Advocate showed as the type of harm of burns was foreseeable, it did not matter that it happened in an unforeseeable way like the explosion. Bradford v Robinson Rentals showed it is not necessary to foresee the full extent of the harm of frostbite. Smith v Leech Brain illustrates the thin skull rule. The defendant must take their victim as they find them, in this case with pre-cancerous cells in his lip.