Speaking from 2 years experience into PhD program, I can surely say graduate studies may be tiring sometimes. Along the way, there are many moments where you say – “that’s it”. Sticking to what you are doing is most important. Love your work. It does not need for one to be genius to complete graduate studies. Getting focused is the key idea. One should be proactive, keeping in touch with his/her adviser. I did do some blunders during start.
One of the ways to keep your spirit high is to read other grad students’ experience. I do that all the time. At least, I know there are other people out there having same situation as mine. Let me share some of the links I feel are good.