From the beginning, the devil's modus operandi has been to sow the seeds of doubt in the heart of mankind with regards to the plan and intentions of God for them. For example, while God's reason for restraining Adam and Eve from eating the forbidden fruit was to keep them alive, healthy and prosperous, the devil came and told them that God did so because He did not have their good at heart (Genesis 3:4-5). It was this type of doubt that the devil sowed in the heart of Joseph's brothers after the demise of their father. Thank God Joseph was a man who knew the mind of God; He quickly quenched their doubts. For us His children today, God has revealed His plans and intentions for us in Jeremiah 29:11: "For I know the thoughts that I think toward you, saith the LORD, thoughts of peace, and not of evil, to give you an expected end".
This is not an after-thought; rather, this has always been God's intention for us from the beginning of creation (Genesis 1:26). It is therefore a sin to doubt the good in God's motives when He directs us to do something or live in particular way that is contrary to what the devil or the world expects.

Because Joseph knew the mind of God concerning all that happened to him, he rejected hero-worship from his brothers and allayed their fears. He comforted them by making them understand that their negative actions towards him were used by God to fulfil His eternal good purpose in his life. Genesis 50:19-20 thus says: "And Joseph said unto them, Fear not: for am I in the place of God? But as for you, ye thought evil against me; but God meant it unto good, to bring to pass, as it is this day, to save much people alive".
In other words, Joseph was saying to his brothers that it was not they but God who sent him to Egypt for a clearly defined purpose. Paul corroborates this truth in 'Romans 8:28.

The Lord is saying to you that you should stop complaining about what is happening to you now; it is for your good. Things will work out for your good if you continue to love God even in that so-called unpleasant situation, which has a divine purpose attached to it. Once again I say to you: it is for your good, and you will soon know why.