The ability to make decisions on a moments notice is very critical. Sometimes when a person has a lot of different options in front of them, they freeze up. This is why you should get really good at making quick decisions that you are okay with. Spend less time thinking about the yes or the no, and more time thinking about the implications of either side once you have chosen. I once heard the vice chairman of Berkshire Hathaway, Charlie Munger say, something along the lines of “it’s much better to make decisions quickly and change your mind slowly”.
There’s nothing wrong with changing your mind as long as it yields the desired results you seek to obtain. However, if you’re too wishy-washy or indecisive about the initial yes or no, you’ll never make enough progress on worthwhile ideas or goals. This is why it may make more sense to decide right away, while thinking about each aspect of the yes, versus the no. You’ll have plenty of time to weigh the pros and cons after the fact.