That can occur because, say, an excess of capital spending by businesses, or excessive leverage, leads to a sharp correction in investment (and employment), which exacerbates a slowdown which was already under way because of external events. It might occur because some shock comes along which fundamentally erodes business profitability and hence reduces prospects for investment.
It might occur because domestic macroeconomic policies, responding belatedly to serious inflation pressure, are faced with a need to tighten abruptly late in the business cycle. As has been pointed out on several occasions by the Governor, the extent of such problems on this occasion has, we judge, been small.