Thats how its supposed to work and in practice it kinda does, but the people with the money want positive results and the people doing the work have to do what they can to stay alive and relevant enough to actually do the work. Which means that while most scientists are willing to change their minds about something once they have sufficient evidence, gathering that evidence can be difficult when no one is willing to pay for it. Hard to change minds when you can't get the evidence to show some preconceived notion was wrong.