A passage from Seneca
Seneca, On Tranquility of Mind IV
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There is no greater cause of grief than the desire for too many things. Unbounded desires make the mind restless, and a restless mind cannot be tranquil.
Related passages
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Your present opinion founded on understanding, your present conduct directed to social good, your present disposition contented with everything that happens — that is enough.
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Everything you're trying to reach — by taking the long way round — you could have right now, this moment. If you'd only stop thwarting your own attempts.
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If thou wouldst be at rest, do little. But it is better to do necessary things, and as many as the reason of a social animal requires, and as it requires.