I have just read this in Thomas Kuhn’s The Structure of Scientific Revolutions (towards the end of XII. The Resolution of Revolutions):
The man who embraces a new paradigm at an early stage must often do so in defiance of the evidence provided by problem-solving. He must, that is, have faith that the new paradigm will succeed with the many large problems that confront it, knowing only that the older paradigm has failed with a few. A decision of that kind can only be made on faith.
More later.