A long time ago a German cartoonist named
One of his stories inspired me to coin the term The White Water Lily Effect (der Seeroseneffekt). Let me explain what this means. Projects tend to go off limit. Everything takes at least twice as long as estimated. And the estimations themselves turn out to be too optimistic, which does not change the truth in the sentence before. Fred Brooks discussed this problem for the area of software engineering in his wonderful book The Mythical Man-Month. In my opinion, user experience is no exception.
Most, if not all UI problems get larger during the time you are working on them. To a certain extent this is natural because you get more deeply involved and gain a better understanding of the issue. You discuss the topic with colleagues and incorporate their point of view into the design. You discover new aspects that somehow match your topic. No big deal to cover them as well. Oh, there is not just your product; so what about consistency issues? Get some information on this. A certain technology might be crucial for your corporate strategy. Still, you have to think about cross-platform issues. I18N, L10N, G11N, A11Y, not to forget W10N and H16T. Are you still with me? W10N is "Way cool design", "High quality product" the latter.
If that is not enough for you, consider that your problem is not the only one in the world. You have a flock of issues on your plate and you contribute to a bunch of other areas, too. The challenge is to keep the chunks of UI problems you address manageable. At the same time you have to keep an eye on the overall structure of the product.
I assume you have an idea of what I mean when talking about the white water lily effect. It poses an omnipresent danger. Being aware of this phenomenon is the first step to come out on top at the end.
Have a great Summer!