This is the question that has killed more brain cells in the history than any other did
Is time travel possible?
Well it is possible at least a few millisecond's in future. In an experiment performed in LHC(Large Hedron Collider) scientist accelerated some particles to 99.99% of the spped of light which increased the life of the particles by few millisecond than their real life. So in a nutshell yes they traveled few millisecond in future(Bloddy time travellers i hate them)
So is problem for us to travel?
Well there are ton's of them so let us as much i know about them
Travelling in the past
Every human being or most of them (don't know much about animal's maybe they also have) have a hardcore desire to travel back to the past and meet their loved one's whom they have lost or waarn them about the calamities that are going to come. Well there is a very pardoxing paradox in travelling to the past. Here try to understand this..
Neo the time traveler
To the Past
Ok let say Neo have found a way to travel back to future and he is a mad scientist. So he makes a portal to go back in time. Let's say he just wan't to go only 5 min back in past and wan't to kill himself (I told you he is mad). So he is now assembling gun part's in front of the portal gate of his time machine. So it takes him about 5 min to do that. So now as he is ready to kill himself in the past he switches on the portal and set it to go 5 min in past. So portal is on and he see's himself through the portal 5 min back assembling his gun (ooo i look handsome). So no he takes his gun(the present one) and shoot's the Neo which he seeing through the portal in the past. Ok so mission accomplished. But now here the paradox arises. Neo in the present killed the Neo who was assembling the gun in past but wait a minute if he was killed while assembling the gun, then how was he able to assemble the gun and switch on the portal and then kill himself (O_o). This is paradox. Like if you go in past tell the people that there is 9/11 going to happen so the people will get alert and stop it but if they stopped it from happening then how did you came to know that this is going to happen as it never happened cause they knew about it, but if it never happened then how did you came to know this happened and informed them in the past.........See it just keeps on going on like a feedback happens in the poor sound system in a rock concert in a loop.
To the Future
Travelling in future is much more possible than going to past. But that will be no more useful other that you wan't to skip a long period of time like about 100 years in a time machine (that is for observer's out of time machine for them they will see that you are sitting in the magic box for hundred's of year but for you inside it will be like everything is moving too fast outside and 100 of year will pass in the world yet only few min or sec or day's depending on the machine for you in the time machine) and then you come out of the time machine to live the future.
Now Answer To Your Question?
I decide to check my future, and (god-permitting) I see that I have passed with flying colors. Now, I "come back in time" and enjoy life, and don't study. So, it is just Impossible that I succeed. So, where is the flaw??
This Is Imposible
Yes, it is totally impossible that you go in the future and see what you are doing and then come to past and fix all you flaws. Why it is impossible? Hmm just think that you now sat in a time machine and you travel to the future to you exam hall to see how you are performing. Now how are you even there in the future in the exam hall giving answer to the question's. Few day's before you sat in the machine then who is living your life outside in normal speed as you were in the time machine all the time, you traveled to the future then how can you be there at that time. I know you are getting a little bit confused so try to look at it from a third person's view (that neighbor who always sneak's at you). Ok he saw that you wen't in the time machine to travel to the future. so now you are not there you are sitting in the time machine traveling in the future. Now after 2 day's there is your exam about which you wan't to know so the exam has started now but you are not in the examination hall as you are in the time machine travelling in future now after few minute you arrive their that the one who started travelling from the past to future to arrive at this time but you see you are not there your place is empty ass all the time for 2 day's you were in the time machine (try not to come in front of examiner or you will have to give the exam and you haven't studying anything as you were busy in time traveling). But now you are two day's in future and you only aged few min. so now you live longer at least 2 day's haha
Hope you got what are the paradox of time travelling
If you still don't understand then watch the documentary in the below given link on time travel that also in Morgan Freeman's voice