When I say that I am grateful for wisdom, what I actually mean is that I am grateful for the mistakes from which I learn. Learning from mistakes is often difficult and painful, but not learning from mistakes is worse.
As a child and a young adult, I viewed my mistakes as completely negative, something that I did that was wrong or stupid. In school, making a mistake translated into a poor grade which resulted in a lower class rank or lower grade. Once the test was over, there was nothing more that could be done to reverse the grade. This resulted in working hard to pass the test but once it was over, moving on to the next subject -- not looking back at my errors.
In "real life" I had to learn what I did wrong, so I wouldn't do it again. If I cooked something at the restaurant and browned it too much - I had to learn not to do that error again. If I lost track of time and didn't have prepared when promised, I learned to budget my time. When painting my house, I learned that the prep work (taping off trim, laying drop cloths, etc) was crucial to having a clean and professional job.
I am not proud of my mistakes, but I learned not repeat them and I am proud of the wisdom I gained from that experience.
The longer we live, the more we can experience and therefore the more we can learn. I am grateful that I have learned some things along the way.