Writing for the Journal’s Expert Panel on Retirement, Jonathan differentiates between vertical and horizontal investment risk. The former focuses on the highs or lows of global stock markets – and the news and predictions of such always grab headlines. The latter determines how long a retiree’s portfolio can sustain ongoing distributions before stocks (and certain bond types that decline along with them in bear markets) would have to be sold, regardless of market conditions – and matters a whole lot more when sustainable income generation is paramount.