You are playing a game on your phone or your computer. You are given certain tasks, when you complete them as per the set rules, you get rewarded with points. As you complete several tasks, you are sent to the next stage. Things get better. You are finally declared a winner and you feel happy.
Now think of your work. When tasks are given and you carry them out as per the set rules. But midway through the task, the rules are changed. The expectations and goalposts keep changing. When you are doing one task, there are two other tasks given towards you. So, you lose focus on the main task. And then there are team members who speak and act in a contradictory way. They are confused and they confuse you too. The people to work in your team do not turn up or they do wrong things. Finally you get blamed for everything. This is when you lose motivation to do any more work!