You could imply that "The Lord is my Shepherd, I shall not want" is a cause-and-effect, in which case the contrapositive would also be true, but even so, many translations cite Psalm 23 as "The Lord is my Shepherd, I shall not be in need." We certainly all as humans "want" certain things, but with God's presence in the believer's life through the Holy Spirit, that is all that we truly need. I understand it may not feel like we have everything that we need when we are in financial difficulty or depression or other issues, and that also doesn't mean we sit back and don't take advantage of the tangible earthbound aids that God provides through other believers, but if we can stand above the fray and look at things from God's perspective and rest in His arms as the Good Shepherd, our terrestrial problems get minimized as we experience His comfort.