Most claims that an intervention will make you 100% better or that it works for everyone turn out to be wrong.
The effects of some treatments 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 interventions are not that obvious and most social welfare interventions do not work for everyone.
That is why we need fair comparisons, for example comparing what happens when people receive the intervention to people who do not.
BEWARE when someone says that a treatment is “100% effective” or that “it’s obvious that it works”.
REMEMBER: Few treatments have such obvious effects that we do not need fair comparisons to know how helpful they are.