Planning fallacy

Planning fallacy makes it hard to estimate how much time a task will take. It happens when people think that a task will be finished quickly, even if past experiences tell us that it might take longer. For example, let's pretend that you have to clean your room. Planning fallacy would make you think that it will only take 10 minutes, even if you know that it usually takes 20 minutes for you to finish the job. It is like you are hoping that it will take less time this time - even if you know that it probably won't!