There are many things we need to recognize immediately as impossible. It is impossible for me to become a player in the National Basektball Association. It is impossible for me to jump tall buildings with a single bound. These appear to be impossible because of my physical limitations. They are actually impossible because I have no calling to do them.
God often calls us to what appears to be an impossible task. He called Moses, a known murderer, to lead His people away from the most powerful ruler on the earth. Elijah was called to see God send fire from above to light an altar before His people. Jesus called Peter to join Him in walking on the sea. Lazarus was called to walk out of a tomb after being dead for four days. Each of these things appeared impossible before they were done.
God's calling to do something is never impossible but it may be difficult. The difficulty arises when we must continue to believe it will happen when it appears impossible.
For example, you have been smoking for thirty-three years. You know that God has called you to quit. At first you tell yourself of all the people you know who have quit. You say, "If they can do it. I can do it!" You really mean it and throw away all your cigarettes. Two hours later you tell yourself you are going to beat the addiction. Four hours later you are nervous about it. Six hours later you buy a pack and tell yourself that it is impossible. Is that true?
Difficult becomes impossible when we no longer believe that God will empower us to succeed. It takes faith to see difficult become victory. It takes assurances from God that He will strengthen you to see what only He can do.
Peter started walking on the water until he remembered that men can't walk on water. He saw the wind and the waves and started to sink. He took his eyes off of his Lord and no longer had the power to walk on water. He was doing the impossible. The difficult part was forgetting that it was impossible.
Maybe you have been called to go back to school. Are you calling what will be difficult impossible? Maybe you have been called to lose weight. Are you calling what will be difficult impossible?
You know what you need to do: Commit what God has called you to do to Him. Pray that He will empower you. Enlist a group of friends you will be accountible to. Choose those who believe. You don't need doubters. Set up short term goals and track them. Then, praise God for your progress. You will see what appeared to be impossible become difficult and then, victory.
Go for it!