Most claims that an intervention always works turn out to be wrong.
The effects of some interventions are obvious. For example, it is obvious that using a parachute is a good way to avoid dying when you jump out of a plane. However, the effects of most environmental choices, for example changing what you eat to reduce your environmental impact, are not that obvious. That is why we need fair comparisons, for example comparing impacts when people eat meat to what happens when people do not.
BEWARE when someone says “it’s obvious that it works” or “has an impact”.
REMEMBER: Few interventions have such obvious effects that we do not need fair comparisons to know when and where they are useful.