This is the 574th most frequent Chinese word.
未能
"未能" means "unable to" or "failed to."
'未能' here expresses the inability to achieve the action '如期到达目的地' (arriving on time) due to external circumstances (天气恶劣). It implies an outcome of not being successful in a particular task despite possible intentions.
由于天气恶劣，我们未能如期到达目的地。
Due to harsh weather, we were unable to arrive at the destination on time.
In this context, '未能' indicates the failure to accomplish '完成这个项目' (completing the project), with a focus on personal efforts or responsibility involved.
他未能完成这个项目，感到非常自责。
He was unable to complete this project and felt very guilty.
Here, '未能' signifies the unsuccessful attempt or inability to perform '正确回答所有的问题' (answering all the questions correctly) within the context of a specific event (an exam).