Forms of the word "sufficient" appear a total of six times in Paul's epistles, curiously all in 2 Corinthians.
2 Cor. 2:7, "Sufficient to such a man is this punishment, which was inflicted of many."
2 Cor. 2:16, "To the one we are the savour of death unto death; and to the other the savour of life unto life. And who is sufficient for these things?"
2 Cor. 3:5, "Not that we are sufficient of ourselves to think any thing as of ourselves; but our sufficiency is of God."
2 Cor. 9:8, "And God is able to make all grace abound toward you; that ye, always having all sufficiency in all things, may abound to every good work."
2 Cor. 12:9, "And he said unto me, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me."
Five of the six references point to God as the source of our sufficiency for ministry (2:14 and 3:5 contexts), suffering (12:9), giving (9:8 context), and everything else he's told us to do (2:14, 9:8). But 2 Cor. 2:7 stands apart in the sufficiency that it refers to: sufficient punishment! I believe that the man referred to in this passage is the erring brother in 1 Cor. 5, whom Paul commanded the Corinthian church (the "many" of 2 Cor. 2:7) to deliver to Satan "for the destruction of the flesh," i.e. progressive chastening (cf. 1 Cor. 11:30). Evidently God answered the church's prayers, something did befall the brother, and he repented.
It's interesting that Paul chooses the word "sufficient" in this context, considering the positive contexts of the other uses. I think, however, that there is a truth here not to be overlooked: just as God's grace is sufficient for us in ministry, sufferring, giving, and all well doing, so is God's judgment is sufficient to correct us...if we'll allow it to. Two professing brothers in Christ, Hymenaeus and Alexander (1 Tim. 1:20), were evidently teaching false doctrine in Ephesus (1 Tim. 1:3), and Paul prayed for them in the same manner that he told the Corinthians to for the erring brother ("whom I have delivered to Satan..."). Notice the purpose of Paul's prayer, though: "...that they may learn not to blaspheme." So Hymenaeus and Alexander had to learn something from the punishment they were receiving to be corrected. Likely the erring Corinthian brother did, from the context of 2 Cor. 2:7, but likely Hymenaeus didn't, since he's still teaching false doctrine in 2 Tim. 2:16-18!
In closing then, this survey of Paul's references to sufficiency in his epistles show that not only is the grace of God sufficient in believers' lives, but the judgment of God, where necessary, is also sufficient for their correction. Thank you, Lord, for loving us so well.
To God only be glory