Jesus was the son of God and He was tempted how much more us. Satan does not mind fighting us when we are weak. How easy it is for us to doubt? If Satan can say to Jesus if he is the son of God what will he say to us. Being a disciple does not make us immune to temptation.
God administers His grace in different ways and in different time of lives. We can see other people being blessed and we want that too. And we begin complain to about why someone is blessed more that we are.