With the concept of yin and yang so central to Chinese thought and Taoism in particular, it is not surprising to hear Lao Tzu (Laozi) teaching its value frequently in the Tao Te Ching (Dao de jing).  In chapter 3, he talks about how reaching any extreme draws the opposite extreme, as in his three examples of traditionally positive values:
TAO
MANOR
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"Do not honor the worthy,
So that the people will not contend with one another.
Do not value hard-to-get goods,
So that the people will not turn into robbers.
Do not show objects of desire,
So that the people's minds are not disturbed."

-- from chapter 3, E. Chen (tr.)
Moderation
In chapter 4 (and echoed in 56), further examples show how Tao tends to bring things from their extremes to a more moderate position:
"It is said that sadness and happiness are corruptions of Virtue (Te); joy and anger are errors of the Tao; goodness and evil are contrary to Virtue.  So, for the heart to be without sadness and happiness, is to have perfected Virtue."

-- from chapter 15, Palmer/Breuilly (trs.)
Chuang Tzu makes a similar point about maintaining moderation in our emotions:
"It blunts the sharp,
Unties the entangled,
Harmonizes the bright,
Mixes the dust."

-- from chapter 4, E. Chen (tr.)
I used to fear the loss of joy that the Taoists prescribe, but living a more moderate life has the benefit of not falling into deep depressions either, and over time, one starts to recognize that expectations are reined in so that what was once barely perceptible satisfaction seems more special.  The more vast mood swings of a life of drama are replaced by lots of little surprises.  None are particularly good, even if they meet our current needs or expectations, because the circumstances will change again in time.  None are particularly bad, even if they run counter to our perceived current needs, because they simply mean that we have been directed toward a different path more in the flow of Tao.