Reason behind Standard Deduction?

hi! can any one tell me what is the real reason behind the so called standard deduction. is it a means of the institute to only pass on the best of the best students to the next level? but by doing so it plays with the aspirations of the other hardworking students! I was quite hopeful of passing this time (2nd attempt) but I only cleared group-II, it is really frustrating, I have not failed but my total is not coming to 300!