Such secrets are always eventually revealed.

One day he will return to Japan.

There will always be things I will never learn, I don't have eternity before me!

There are many regrets in a person's life. It's not possible to do everything well.

There are always some people who are unreasonable.

Language can sometimes be very complicated and worry us greatly, especially when we cannot express what we want to say, but there will definitely be a day when we can communicate well.