A lot of projects go wrong because they're just too big, you may have heard people say that the. For example, if you have 3 features you want to add to your website we might do 3 different releases, each one would be an iterative improvement of your website.
By making iterative improvements, anyone coming to your website will benefit from all the new features which are finished. Your users shouldn't wait for 'feature 3' to be completed before they benefit fro 'feature 1'. This is particularly powerful if you're carefully prioritising the features to give the users the best experience.
Whenever we approach a new project or an enhancement to an exist project, we break them down into things the user cares about. We then build them in 'iterations'. Once you're happy with it, we show it to the world.
We've got systems in place to make it easy and reliable to keep on putting out new versions. That way, we can be confident that the new version will work as expected.