The accepted wisdom on 'causation' was, and mostly is, the 'but for' standard. It stems from the philosophy that delineates 'necessary' and 'sufficient' causes. A 'necessary' cause is one that amongst others has to be present for the effect to take place, and a 'sufficient' cause is one that by itself can create the effect. A 'but for' cause is a human-created necessary cause - that is, without ('but for') that human-created cause the effect would not have happened, and so the human that 'did it' is typically legally responsible for the harmful effect.
Mind you, with law being a thoroughly social activity, it's not always quite so simple. Even when not dealing with 'proximate cause' (aka 'cause-in-law'), which is causation that openly modifies itself by social factors (eg. remoteness and proximity), causation is inherently a social creation - not a feature of physics. It can often be a complex and uncertain matter.
