The technical aspects of creating a web site grow in complexity as businesses demands increase and consumers become more sophisticated. Unless you are building an internal Intranet you have no control over how your web site is being viewed. You have no way of knowing what size monitor, resolution, browser, browser version they are using or even if they are using a computer at all. People can also access web pages through televisions, webphones, pagers, voice browsers and who knows what next. You also have no way of knowing where in the world your visitors are coming from, if they speak English, have physical limitations or if their intentions in visiting your site are friendly or hostile.
How much of these aspects are taken into consideration when developing a site can greatly influence the extent of your reach into cyberspace. It also impacts development time and cost. Like many other aspects of web site development, robustness is not an all or nothing decision. Various technical aspects of site development should be understood so that informed decisions about robustness can be made. What is robustness? Simply put, it's how 'bullet-proof' your web site is - how well it performs under a variety of conditions.