Ecclesiastes 2:12

Next, I considered wisdom, as well as delusion and folly. What can anyone [do] who will come after the king that has not already been done?

Ecclesiastes 1:17

So {I dedicated myself} to learn about wisdom and [to] learn about delusion and folly. However, I discovered that this also [is] chasing wind.

Ecclesiastes 7:25

I set my mind to try to seek wisdom and the plan, and to know that wickedness [is] foolishness and that folly [is] delusion.

Ecclesiastes 1:9-10

What has been--it is what will be; what has been done--it is what will be done; there is nothing new under the sun.

Treasury of Scripture Knowledge

Summary

And I turned myself to behold wisdom, and madness, and folly: for what can the man do that cometh after the king? even that which hath been already done.

Even that which hath been already done

Bible References

I turned

Ecclesiastes 1:17
So {I dedicated myself} to learn about wisdom and [to] learn about delusion and folly. However, I discovered that this also [is] chasing wind.
Ecclesiastes 7:25
I set my mind to try to seek wisdom and the plan, and to know that wickedness [is] foolishness and that folly [is] delusion.

Even that which hath been already done

Ecclesiastes 2:25
For who can eat [and drink], and who can enjoy [life] apart from him?