ことはない is a sentence-final pattern that has two main uses. The most common is to say that there is no necessity to do something, similar to 'you don't have to' or 'there's no need to'. For example, if a friend is worrying about something trivial, you can say 心配することはない (You don't need to worry). This use often carries a nuance of reassurance or telling someone not to bother.

The second, less common use expresses that there is no possibility of something happening. In this case, it attaches to the dictionary form of a verb, as in そんなことがあることはない (There is no possibility that such a thing happens). This usage is more formal and often found in written or careful speech.

It is important to remember that ことはない is a fairly formal expression. In casual conversation, you might hear it, but it can sound a bit stiff. For everyday speech, you could use なくていい or する必要はない for 'no need', and はずがない for 'no possibility'.