Only bu being forced to defend an idea against the doubts and contrasting views of other does one really discover the value of that idea.
怎么分解?
Only by( being forced to defend an idea against the doubts and contrasting views of other )does one really discover the value of that idea.
还是:
(Only bu being forced to defend an idea against the doubts) and (contrasting views of other )does one really discover the value of that idea.