N.T. Wright comments on the fruit of the Spirit:
The "fruit of the Spirit" does not grow automatically. The nine varieties of fruit do not suddenly appear just because someone has believed in Jesus, has prayed for God's Spirit, and has then sat back and waited for "fruit" to arrive. Oh, there may well be strong and sudden initial signs that fruit is on the way. Many new Christians, particularly when a sudden conversion has meant a dramatic turning away from a lifestyle full of the "works of the flesh," report their own astonishment at the desire that springs up within them to love, to forgive, to be gentle, to be pure. Where, they ask, has all this come from? I didn't used to be like this. That is a wonderful thing a sure sign of the Spirit' working.
But this doesn't mean it's all downhill from there. These are the blossoms; to get the fruit you have to learn to be a gardener. You have to discover how to tend and prune, how to irrigate the field, how to keep the birds and squirrels away. You have to watch for blight and mold, cut away ivy and other parasites that suck the life out of the tree, and make sure they young trunk can stand firm in strong winds. Only then will the fruit appear.
And, in case anyone should think I am imposing an alien note on Paul's cheerful list of these wonderful characteristics... we note the final characteristic in the list: self-control. If the "fruit" were automatic, why would self-control be needed? Answer: it isn't, so it is: it isn't automatic, so it is needed. All the varieties of fruit Paul mentions here are comparatively easy to counterfeit, especially in young, healthy, happy people -- except for self-control. If that isn't there, it's always worth asking whether the appearance of the other sorts of fruit is just that, an appearance, rather than a real sign of the spirit's work.1
1. N.T. Wright, After You Believe: Why Christian Character Matters [Harper One: New York, NY; 2010] pp. 195-196