"In the LORD I put my trust . . . "
Because David put his trust in the Lord, he was not ultimately moved by what happened around him down here on earth. The "foundations" may be "destroyed," (v. 3)--but he would nonetheless press on, basing all of his life in his faith in Christ.
And so it should be for us, as well. Circumstances--particularly, negative ones--are sure to impact us, and affect us--but we should not be too disturbed by them. When it is all said and done, at base, the only One we have to lean on is God Himself. This is not an easy thing to do--but the more we succeed at it (by grace), the better off we will be.
[Puritan quote of the day: "In a hopeless estate a Christian will see some door of hope opened . . . " --Richard Sibbes, in, "The Soul's Conflict with Itself"]