I know you are all thinking "Not this again " but just hear me out . Get ready for a good mind fuck .
I have watched most of the time travel movies that have came out in the last 30 years , so I have thought a lot about it. What I have came up with is this . If they had succeeded in changing what was bad , would the bad thing have happened in the first place , there would have been no need for them to have gone back in time . If you see something bad and you say to yourself "I will go back in time to change that " and you need to think it anyway it means that you failed to fix it in the future , or that moment wouldn't have happened .
You need to think about this , what is the same thing about all time travel movies ?
The same thing is this , in all time travel movies there is always a problem that leads them into the past in the first place . If they go into the past to fix something they did wrong , and succeeded , then wouldn't that also stop the moment that they think of going into the past to fix it from happening , also stopping them from going into the past to fix the problem in the first place .
Time travel is just one big circle , nothing is ever changed cause if they go back in time to change something its stopping them from having the thought of time travel in the first place .
The only movie I have seen that has anything close to my thoughts on time travel is " The ButterFly Effect " .