One of the most common points of friction between project managers and developers is planning work. Most programmers hate creating work breakdown structures (WBS). You can't blame them, accurately predicting steps and effort required to build undesigned software is impossible. Yes, you heard that right. Software development planning is impossible — at least for someone who likes precision, which most programmers do.
The problem is that every software development project is a unique collection of thousands of tiny details that each have the potential to suck up enormous amounts of time. The traditional, PMI-sanctioned WBS technique forces developers to name all the activities that will be required, sequence them with dependancies, and then create an estimate of each one. The assumption is that if you did the planning right, you should just be able to follow the steps and come out the other end on time and on budget. This also implies that if you didn't blindly follow the steps, the project plan was wrong — or you were too incompetent to follow the steps correctly. But with the fluid nature of software development, the project plan is always wrong. I used to think that precision would increase with finer granularity. The more lines in the project plan, the more accurate it would be. But now I think the opposite is true. The more tasks you add, the more guesses you make and the greater the overall variance. Even if you guessed every task right, there were probably just as many tasks that you forgot to add. And there are also lots of steps that you find you didn't need to do too.
While predicting a WBS is impossible, developers can get better at setting and meeting deadlines. There is a small nuance between setting a deadline and estimating tasks in a WBS. On the outside, the difference is so small that no one will notice. Nobody will care because they just want to know when the work will get done. But there is a difference. The WBS technique forces a linear accounting of all the work that needs to be done. Creating a deadline is more like adding a constraint (that you hope is reasonable) to help guide and prioritize the work that you wind up doing. Comparing the two is like comparing launching a rocket to flying a plane. PMI-style planning is like shooting a rocket: doing all the calculation at the beginning and then hoping that you accounted for everything before ignition. Setting a deadline turns the rocket into an airplane by adding a pilot that can steer. Realizing you can make adjustments after take-off transforms the pre-flight calculations from a fixed flight path to a map that you can use to make in-flight decisions. A deadline (either the final deadline or an intermediate milestone) is where you think you can be at a certain point of time (or after a certain amount of effort). When creating a deadline for yourself, you don't try to think of every possible task it will take. It is more like eyeballing distances than counting steps.
I became conscious of this distinction the other day when I was on a bike ride. I take pride in the fact that I usually get home within a few minutes of the time I tell my wife I will be back. Lots of times I pull in right at the minute. Putting on my planner hat, if I was asked how long a bike ride would take, I would want to know the exact route and measure the distance and slope and windspeed and make assumptions about average speed. When I put on my cycling helmet, I realize that most of those variables are under my control. I can shorten the route. I can ride faster. I can take an alternate road to stay out of a headwind. Because I know my cycling ability and the terrain so well, I make these adjustments without even thinking about it.
I know you are thinking that software development is not like riding a bike. There are all these externally imposed requirements, constraints, and dependencies that need to be accounted for. But think back and ask yourself: how many of these factors are added specifically for the purpose of creating the WBS? I feel like developers work against themselves by asking for more and more estimation inputs and being more prescriptive of how they will work. There is no way that every detail can be accounted for and every detail that you do add will constrain your ability to make adjustments.
For estimation purposes, requirements should represent boundaries of an acceptable solution. With this understanding, a developer needs to produce a reasonable deadline based on similar work and explain any assumptions made. An overall deadline or intermediate milestone shouldn't be overly ambitious. It should account for unknowns. If a deadline is not acceptable, scale back the scope until an acceptable deadline can be achieved. Through the course of the project, new information is going to present itself: the client is more particular than he was able to articulate; the available components are not as good as expected; new features are added to the scope. When any of these things happen, you make adjustments. You might be able to work a little more efficiently. You might be able to scale down scope in other areas. You might be able to delegate work back to the client. Or, you might just have to extend the deadline.
These adjustments require a decent partnership between the developer and the client where the deadline is jointly owned. It doesn't work when one party feels like the other is obligated to deliver no matter what. In the bicycle analogy, when two people go for a ride, they decide where they want to go. Usually the conversation plays out where one rider asks the other what sort of ride he is up for. The second rider may say he needs to get back in 2 hours and wants to get in some climbing. The first rider will suggest a route that he is familiar with. When they encounter construction that makes a road impassable, they may be able to find an alternative route that is just as good; they can hammer home over a longer route in a paceline; or they can call home to say that they are going to be late. Whether the first rider should have known about the construction is debatable (Did the construction just start? Was the overall distance to ambitious? Did the route not allow for adjustments?) but debating is not going to get anyone home sooner.
With experience, you do get better at making more realistic deadlines. And, more importantly, you also get better with time management. You will build an awareness of where you are in the overall process and know early if you are falling behind schedule. In the cycling analogy, you periodically glance at the clock, your current speed, the slope of the road, and which way the wind is blowing. In software development, you are looking at things like the calendar, the productivity, and the rate of defect identification. With this information rolling around in your subconscious, you start thinking about options instinctively. The client perception is that you planned well. But you really didn't. You managed time well. The up front estimate was just one of the many constraints that you juggled when developing the solution.