Just like the importance of our bodies being flexible in order to deal with the day to day movements, it's also important to be flexible with plans and tasks. Life happens. You need to look at everything that comes up and decide that nothing that happens is good or bad. It just is.
Don't decide that a spilled cup of coffee is a good or a bad event, it is just an event that happened.
Once you decide not to label things as good or bad, you become more flexible in your thinking and your outlook.
It takes practice, but you can do it!