Why must science be open to change?

 everything in science is all based off of  a theory because there isn't enough evidence to prove it to be a fact. So,if more evidence is discovered to prove it,a theory will become a factual,or if evidence is discovered  against it, aka disproving it  a theory, the theory is no longer even valid as a theory because theres factual evidence against it. so, knowing this scientists have to be open to new ideas in order to find out the "truth" or to build upon.