Gathering Requirements is an INVESTMENT
Most important part of a project success is : Requirements . Requirements is the Goal . it is "What we are going to build" . and because ot its importance , alot of studies have been done on relation ship between investment in requiremetns gathering and failure of projects.
NASA found that there is a deep relationship between requirements investment and cost overrun of projects. you can read their guidance on their site for that .
bottom line , "Gathering Requirements" is an INVESTMENT .