How many times at work have you planned a project only for it to take 2 or 3 times the time you expected it would? Or how many times do you actually hit a self-imposed deadline? I would imagine very rarely. This becomes even more important when you are working for yourself, planning your days and how long you expect to be working on specific areas of your business.
People’s poor ability to estimate how long it takes to do things is referred to as the Planning Fallacy and was demonstrated by Kahneman and Tversky experimentally. One possible solution they identified to resolving the issues resultant from this fallacy (apart from at least being aware of it in the first instance) is to split your tasks up into as small a component as you can and estimate upwards from there.
For example, if you need to draft wireframes for a website, don’t start by saying “oh this should take 50 hours”. Start by working out how many screens you need to make, then if possible, time how long it takes you to make a test screen (preferably a more complex one), extrapolate that then add on a contingency time (say 10%). While this is unlikely to be a flawless estimation technique (as you may come up with unforeseen issues along the way) it will give you a much more accurate idea of how long the task will take, it will allow you to better plan your days and better communicate with other team members as to when they will be able to work on certain areas. Delays can have huge knock-on impacts on other people on the project and so it is your responsibility to be mindful and reactive to this.
Now take that finger out of the air and get your calculator out.