How did Phineas gauge's brain injury help psychology?

Because the case study had shown that even with the most traumatic events that can happen to your brain, there are still possibilities of you staying alive. And even if changes in behaviour and personality have not changed straight after (this particular trauma) they will be picked up on as life goes on. For example; Phineas Gage's behaviour did not change as soon as the accident had happened although changes that were stated as 'childish' from his doctor were picked up on four months later prior to the accident. With this his doctor had to tell family, friends, relatives and co-workers about this; which later resulted him not being able to be employed again.