了然于心的英文怎么说

了然于心的英语可以用 "to be thoroughly understood or grasped" 来表达。

这个短语是来自英文 "to be thoroughly understood" 和 "to be grasped" 两个短语的合并。"to be thoroughly understood" 意思是 "完全理解"，"to be grasped" 意思是 "被掌握"。

下面是一些例句：

The concept was difficult to grasp at first, but eventually it became thoroughly understood.
这个概念起初很难理解，但最终我完全理解了。

After reading the instructions several times, the instructions were thoroughly understood and the task was completed successfully.
经过几次阅读说明，我完全理解了说明，并成功完成了任务。

It took a while, but the new software was eventually grasped and is now being used efficiently.
虽然花了一段时间，但新软件最终被掌握，现在正在高效使用。