A: I got stuck, I am the stupidest in the world, I can’t find the answer ever, and I really feel bad.
B: Are you a graduate student?
A: How did you know!!!!
There are common symptoms for this kind of disease, “being a graduate student”. Doing a research is tough but more than that is to learn how to do it. You need to be patient and at the same time you should avoid being too picky. You need to be aware where you are and try not to diverge from the main research stream, which is the supervisor responsibility to watch you not getting lost (if they bother).
You are going ups and down all the time; they are some times that you feel the lowest IQ in the world is yours, you can’t do anything and completely stuck.
This is to all other graduate students of the world if you have the same feeling don’t worry. This is the same for every other one. Depends on their personality some grads show it and some don’t. All of us feel unsure many times during our research program. Good luck to all of us.