Time Machine. What Do You Want To Change From The Past?

Hi! It would be wonderful if time machine does exist, mainly for research purposes and such. Though, I must admit that not only once I wish there were some way I could go back time to change something. If only I could change the time I made the decision when I quit my job. But you see, if there is indeed a way to go back in time and change something, then there would be a riot :) I imagine, a lot of people will no longer think about what they would do or the effect of their decision in their future since they will always have an option to change it thru time machine. People will no longer regret whatever they did because they can always go back to correct it. But time machine is wonderful nonetheless to explore the life of the past or our ancestors.