The art vs science debate: Why can’t we fully embrace creative effectiveness?

“Perhaps the single most important word in the lexicon of advertising is ‘test’... Testing new ideas, new headlines, new media combinations. Test, test, test. That’s why everyone should start his advertising career in direct response, because in direct response, you test all the time.” David Ogilvy. 
Since the 1960s, the ‘father of advertising’ talked about new opportunities for creatives to understand what makes people tick, new creative iterations