Sentence:  The dirty secret of the internet is that all this distraction and interruption is immensely profitable. Web companies like to boast about [...], or offering services that let you... "share the things you love with the world" and so on. But the real way to build a successful online business is to be better than your <WSD>rivals</WSD> at undermining people's control of their own attention. 
Meaning of the word marked with <WSD> tags:  A competitor (person, team, company, etc.) with the same goal as another, or striving to attain the same thing. Defeating a rival may be a primary or necessary goal of a competitor.