Motivation break down~

Sorry to put such a negative title for this post, but it was what I felt yesterday. Morning meeting went good in term of help my professor was offering me, but not well in term of the relevance of my research. So, I began to feel bad. And then it came my best friend's presentation (to all faculty and advanced grad students). It went bad.... they criticized him about the motivation of his paper. Put it crudely: "why are you doing something that you don't even know why and what for? what's the point to do something so complicated computationally for no purpose at all?" And then his adviser told him that if he can't come up with a good argument, he needs to change topic for his dissertation proposal. oh... God! I don't be in his place!!! And I'm presenting in less than a month. I had an idea and a good motivation I think, but I kind of couldn't put all pieces together to say okay, this is what I want to explain and that is how. I know that I'm not in a bad situation... but you know when your negative thoughts trigger the chain of negative thoughts...it's hard to stop. The reason that I felt so bad is because I make the little obstacle a really big life threat. And then I made me to think I’m a looser, that I don’t worth appreciation from my professor, that I’m a useless person, that I got into grad school by mistake… etc. When I think about it more, I feel worse. But I know that when I am positive, all these negative thoughts disappear right away and this little obstacle might be a good thing to help me to achieve something bigger. I know all that... it's just hard to do it. Maggie wrote a inspiring post yesterday related to this kind of feeling.
Let me finish this post with pic of my yesterday's eats and let it self explain.
Sorry to everyone for such a negative post, I hope I feel better today so I go to Argentina motivated and happy so I can enjoy it more.