Proverbs 23:7 "For as he thinks in his heart, so is he...."
In life, we are often surrounded by negative news, negative things, negative friends, and sometimes you might be in a negative family. This will indirectly influence our character, just as the bible says, "For as he THINKS in his heart, so is he..".
As medical reports suggests, your psychological thinking will indirectly influence your health too. There is a case where medical reports of two different patients were swapped accidentally, one of the patient is confirmed diagnosed as terminally ill patient while the other does not. In the end, as the healthy patient got to know that he is diagnosed to be terminally ill, his heart kept on thinking that he will die and be very negative, truly, not so long after that, the patient passed away; On the other hand, the true terminally ill patient did not know he has cancer so he is very happy and eventually he live a healthy life onwards.
What you think could influence you yourself!
In other words, the opposite is also true, POSITIVE thinking will make us to be a POSITIVE person! It is what Jesus' character is too.
Application:
1) "What should I do if I could not cope with my studies?"
--> "I must be able to get through this, God will give me wisdom and understanding to study about this!"
2) "Oh, no I will not be able to do this properly since this is my first time"
--> " I will try my best to do this although this is my first time!"
3) "Oh, today is raining, I think I will not come to church."
--> " Oh, today is raining, it is not too hot. I should go to church."
4) ... so on.