Nairn RobertsonMarch 12, 2014Why things takes longer – probability hates youWhen you think about why things often take longer than you originally thought, there are some reasonably obvious reasons which jump out. But there is one hugely significant reason which most people don’t consider. Understanding this reason is important for anyone interested in getting things done.Originally I titled this “variance is not symmetric” but that wasn’t as catchy as “probability hates you”. Variance is not symmetric, may sound a little complex but it is in fact rather simple (although a little difficult to explain…bear with). Essentially when we break things down into individual tasks, we expect that some tasks will take a bit longer and some a bit less. Overall we hope they’ll balance out and you’ll finish on time. Graphically this would look like this (apologies for my rusty photoshop skills):Importantly the area to the left of the line (early) is equal to the area of the right (late) which basically means the probability of being a bit early is equal to the probability of being a bit late. It’s all in balance. The truth is not symmetrical In real life though, the graph is not symmetrical. Consider: There is a limit to how early a task can be, but no limit to how late a task can be. Or put another way: There is no maximum limit to how long something can take, but there is a limit to how little time something can take. When applied to lots of tasks I’m afraid this works against us.Imagine you estimate two tasks will take two hours each. Total time is four hours. So you crack on and Task One goes badly and takes five hours, so overall you are running three hours behind. Ouch, maybe Task Two will make up the time. Fortunately, Task Two goes very well indeed, but it can never take the minus one hour you need to get your three hours back in order to get back on schedule. So no matter how well Task Two goes, you will be late. So I think the bell curve actually looks more like this:The area under the right side (late) is greater than the area to the left (early) which is bad news and why probability hates you. Even worse, theoretically the long tail probably reaches to infinity! There is absolutely no limit to how long a thing can take. So often tasks which take longer than expected are not balanced out by other tasks which take less time than expected. Any single task which takes a lot longer than expected requires many other tasks to go well in order to get you back on schedule.Sorry.Written by Nairn Robertson2 CommentsPosted in estimating, UncategorizedTagged with development, estimating, probabilityFebruary 12, 2014Why we should ‘create’ not ‘build’ websitesBefore I delve in, let me state that I am not a developer. However I studied physics and engineering for four years, have done some coding and have a good sense of logic.  I’ve worked with developers for 14 y