What is Vないことがある?

[Andromedashun]

For example:

朝は電車が込んでいて、乗れないことがある。

My predict is that it emphasize a fact that the speaker can't go in the train?

Thankyou to any help.

[Toritoribe]

Have you learned the structure "the conclusive form(終止形) of a verb/adjective + ことがある", meaning "sometimes/occasionally/depending on the case"？ It's quite the same.

[Andromedashun]

O_0 No, I've never heard of that structure before. Please explain.

[Toritoribe]

朝は電車が込んでいて、乗れないことがある。
I sometimes can't get on the train, since it's too crowded.

疲れているときはタクシーに乗ることがある。
I sometimes take a taxi when I'm tired.

[Andromedashun]

Oh I see. Now it's clear. Thanks again!