Some kids who act hyperactive can be calmed by giving them a depressant. Other kids who act hyperactive get more hyperactive if given depressants. Giving them stimulants calms them down.
Or
Some people with heat stroke will improve if given water. Others will get worse.
All these paradoxical effects prove is that the human perception of symptoms does not have a direct connection to the root causes of those symptoms. It doesn't mean that stimulants or water (or SSRIs) therefore have questionable efficacies.
You could easily write at length on the efficacy of water in putting out fires:
You can put out a campfire with water, but adding
water to a grease fire does the opposite. So obviously
the use of water to put out fires is nothing but hokum!
Or
Some people with heat stroke will improve if given water. Others will get worse.
All these paradoxical effects prove is that the human perception of symptoms does not have a direct connection to the root causes of those symptoms. It doesn't mean that stimulants or water (or SSRIs) therefore have questionable efficacies.