What does Ecclesiastes 9:13 mean?

Whatever your hand finds to do, do it with your might; for there is no work, nor plan, nor knowledge, nor wisdom, in Sheol, where you are going.

I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favor to men of skill; but time and chance happen to them all.

For man also doesn’t know his time. As the fish that are taken in an evil net, and as the birds that are caught in the snare, even so are the sons of men snared in an evil time, when it falls suddenly on them.

There was a little city, and few men within it; and a great king came against it, besieged it, and built great bulwarks against it.

Now a poor wise man was found in it, and he by his wisdom delivered the city; yet no man remembered that same poor man.

Then I said, “Wisdom is better than strength.” Nevertheless the poor man’s wisdom is despised, and his words are not heard.