stumbling-block

stumbling-block
n thing that causes difficulty or hesitation; obstacle 造成困难或引起疑虑的事物; 障碍物; 绊脚石
    The failure to agree on manning levels is a major stumbling-block to progress in the talks. 人员配备情况未能达成协议是会谈进行中的主要障碍.

牛津英汉双解词典