It must be a very stupid question, but since I have not such sufficient know ledge storage and having no more time to search the answer of it, I have to put it here to ask for help. I generated a training dataset of images of simple geometric shapes as triangles, squares, diamonds etc. by programs and constructed a CNN with two convolutional layers and one pooling layer also a final fully connected layer to learn the classifications of these shapes. But the network just does not to learn it. I mean the loss just does not decrease. What is the cause?