Why Say Insha'Allah
Here is my opinion on this matter. Using InshaAllah gets Allah’s will and blessings involved in the matter. As stated in Quran human sometimes asks for something which is not good for him. Also Allah knows our personality and capabilities. When we say InshaAllah, Allah based on his knowledge directs us in certain direction or leads the outcome in certain direction which is good for us in the long run. There is a story in Quran pointing to this fact. If we do not say InshaAllah then things fall as it may without Allah’s intervention and the person has to struggle through it.