不足为奇，大部分有关这些问题的讨论没有涉及TDD、或者迭代，甚至没涉及回顾，因为障碍来自团队的外部。
Not surprisingly, most of the discussion around these problems did not involve TDD, or iterations, or even retrospectives, because the roadblocks were coming from outside the team.
病毒营销免费且实施非常简单，所以用户接受没有任何障碍。而病毒传播是唯一可能的，因为就是这个问题，且比其他选择好的多。
As it was free and dead simple to use, there was no barrier to adoption; but the viral spread was only possible because it was such a big problem and it was so much better than the alternatives.
作者说：没有显示出跟辍学有联系的障碍可能对大学学生的影响较小，因为对学生来说这些障碍产生的问题较少。
Disorders that did not show an association might have affected college students less because they created fewer problems for the students, said the authors.
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