San Jose Business Daily - Why do e-marketers often have difficulty estimating the ROI of a new product under development?

Why do e-marketers often have difficulty estimating the ROI of a new product under development?

please explain using examples.

Some thing may seem to be great in labs, and should have a smooth transition to the public, but not everything always works out. Example, McDonald's Arch Deluxe..
In all honesty, they shouldn't. It depends on the data you're collecting and analyzing from your site. If you have an e-marketer who is able to build actionable reports that track an entire conversion funnel from referrer to conversion and have a solid grasp on avg. cost per conversion and avg value per visitor, it should be a very attainable metric. Sure, there are a good number of variables to consider, but I wouldn't say there are any more than what offline marketers contend with. Audit the reporting process of current usability, cost, and user value. In those numbers you will find your answer.