While the latter category may have been affected by unfavourable external factors, the large number of projects completed later than planned indicates that project planning continues to be too optimistic with respect to time frames.
后一类可能是受不利的外部因素影响的缘故，但许多项目的峻工时间都晚于计划时间这一情况，也说明项目规划在时间范围方面仍然过于乐观。