> If a patient thinks they are on a treatment, they might actually end up healthier than a patient who has just been told there are no treatment options left for them...

Isn't the actual aim? to have someone heal?

> Likewise, if a clinician is really hoping the new drug they are developing is successful, their judgement of exactly how quickly a tumour is growing might not be fully impartial

Well, this is something that is quantifiable I guess (a measurement). And changes must be notable in order to call something a success in that case.