A company's investments can easily ruin the plans of its competitors.Competitive dynamics matter, and often sooner than investors might expect. Eli Lilly's (LLY -0.82%) chief executive officer recently disclosed that the big pharma is positioned to cut off a potential driver of revenue growth for Hims & Hers Health (HIMS 0.06%), and that it will chalk up some growth itself along the way.Here's what's happening, and how it affects the case for an investment in each company.This blocker to revenue growth is r ...