In many ways the point Seneca is making here is one of the most important in Stoicism: since we are striving to be happy - and wisdom is knowledge about how we become happy - it's easy to focus too much on knowledge and think that the basic criteria for when we are wise is how much we know. It's not. The basic criteria for wisdom is whether we are happy.
"Now I will tell you how you may know that you are not wise. The wise person is filled with joy, cheerful and calm, unalarmed; he lives on equal terms with gods. Now look at yourself. If you are never downcast; if your mind is not bothered by any hopes concerning the future; if your mental state is even and consistent night and day, upright and content with itself, then you have indeed attained the fullness of the human good. But if you seek pleasure in every direction and of every kind, then be aware that you are as far removed from wisdom as you are from joy. Joy is your aim, but you are off course: you think that you will get there amid riches and accolades; in other words, you seek joy in the midst of anxiety! You go after those things on grounds that they will bestow happiness and pleasure, but in reality they are causes of pain."
- Seneca, Letters 59.14