Bhagavan only knows the complete picture of our several janmas, our karma bags and our future janmas (if not liberated in the current janma). So, based on that he makes a plan to give us a birth (human birth itself is a rare one) in a particular family, particular varnasrama, boy or girl suitable for easy advancement towards destination.

Krishna solves our 'path to destination puzzle' like a Big jigsaw puzzle by making so many movements. Without questioning and with strong belief in Him and Acharya, if we incline ourselves to be in a place, they show, He can solve the puzzle soon and will make our life and then Atma blossom like a beautiful flower picture.

Krishna has given Gita as a wonderful gift to all. With a proper understanding, we can always enjoy our life with gratitude towards Him for what all we are blessed with. Unanswered prayers mean either what we asked was not good for us or for some long term benefit, we have to  undergo such short term troubles. Just like a mother who won't give her kid, something which is not good for the kid even if the kid desperately wants it, Krishna won't answer our prayers (for worldly benefits) if those won't do good to us. 

During surgery, we can't request doctor for no pain at all. We have to bear the pain thinking of long term cure of the disease. We only know this janma. Krishna only knows our karma bag accumulated over so many janmas. To get rid of those karmas, for the long term benefit of reaching a permanent happy state, He has to do some operations major or minor depending on our karmas. But we will get the power to bear those pain with His smaranam as an anesthesia.