Well it contradicts Rip ' s entire plight in the first season . If the future can be cemented , then he can ' t save his family . If he knows that , why is he doing this ? More than that though , it just doesn ' t make sense . Time doesn ' t work like that . If you make a change , it instantly changes the future and can be just as easily undone . See Flashpoint , if time can be cemented , why could Barry save his mom ? And if time can be cemented how could he go back and let Eobard kill her ? and if time can be cemented how did Eobard even change the future in the first place ? Because his future should have been cemented too . If the future can be cemented , how was Vandal even defeated ? Because according to the rules of cementing timeline , that should be impossible to undo , since it was cemented . I can keep going and going with that . It honestly boggles my mind .