Activist investing is now a mainstream tactic, but while some funds are learning new tactics that have only recently become widely accepted, others have years of experience under their belt. In a recent interview with Value Investor Insight, Blue Harbour Group founder Clifton Robbins explains the approach that has earned Blue Harbour an annualized 8.9% return since its inception in 2004. Think like an owner: Blue Harbour’s Robbins “The company has to be a great investment, fundamentally undervalued and trading at a discount to what we consider to be its intrinsic value. But in addition we have to have ideas…