After getting a number of my estimates wrong recently I was thinking about this question. While walking to work I determined a few things. It's hard to estimat

After getting a number of my estimates wrong recently I was thinking about this question. While walking to work I determined a few things. It's hard to estimate something that is complex. If I am very confident the job can be completed in under an hour my assessment is very close to 100%. This is because something simple does not have a lot of variables and interacts with very few things. Things like fixing a display bug, a simple calculation, adding a print now button are all easy. Once you go beyond this it gets more difficult to determine how long something will take. Business wants the estimate done quickly. Many businesses want estimates done fast. An accurate estimate for a complex job cannot be given fast. There has to be several rounds of back and fourth. Use-case scenarios need to be determined, which will open up even more questions. The underlying architecture to accomplish the feature also has to be scoped which will take time and usually we don't get it right the first time we think about it Some more reasons are, businesses want the job done quicker than is realistic. Businesses don't know everything they want. They think they need stuff that they never end up using. Haven't thoroughly thought out the feature or problem themselves and that uncertainty gets passed into the development phase more often than not. Business is not solely to blame though. Sometimes developers think a particular portion of their code will be simple when its not or difficult when it isn't. Basically the whole process is riddled with human error on both sides.