Here in the UK inflation was 18% in 1980. It's been over 10% several times since then. 4% assumes things will carry on as they have been for the past couple of decades. There's no reason to believe that.
But if you don't hold too much cash/fixed income securities and actually hold equity investments (e.g. real estate, stocks), then why would inflation be a concern? All those investments should easily keep up with inflation by their very nature, or am I wrong?