The best explanation that I have come across is this. Impatience happens when we have setup a goal and then we discover that the goal is going to cost us more than we are willing to spend. Now cost does not have to be money. It can be time or some other resource. When we realize that the goal we have set is going to cost more then we are willing to put in, then impatience starts.
It is the gym story. Repeated over and over again. You are excited about your new goal to look and be healthy. You create a plan to go to the gym and then while at the gym, under the workload of effort and time, you are suddenly thinking, hold on. This is going to take way more time and too much effort for me to invest and so you stop. Impatience kicks in and you start to look for some other means of fulfillment.
This is always the way of it. We decide to go to college. We are all excited about the prospects of achieving something great. Then we show up and start to do the work and we are hit over the head with the magnitude of it all. This is going to take way too much time and effort then I am willing to spend. This is what causes failure. We start to look for shortcuts around the workload and spend more time doing that then the actually work.
When viewing this feeling of impatience through the lens of resource constraint, you start to realize the folly of your goal planning. Every goal must include an analysis of the work load and effort that is going to be required. If you do not have the resources or the willingness to spend the resources, then you will just not fulfill the goal. Your impatience, a protection mechanism, will kick in.
A willingness to spend the time, money or other resource is necessary to overcome impatience.