"If you are distressed by anything external, the pain is not due to the thing itself, but to your estimate of it; and this you have the power to revoke at any moment." (Marcus Aurelius, Meditations)
If you're into self-help and personal development, you've most likely come across the terms stoicism and stoic philosophy a lot these days. Unlike a fancy-sounding pop psychology trend or personal development quick fix, stoicism is a powerful ancient Greek philosophy concept.
It was first introduced by Greek philosopher Zeno of Citium (as far back as 300 BC) as a modification of cynicism which talks about self-control, restraint, and fortitude for combating destructive/harmful emotions. Stoicism in principle doesn't call for completely demolishing emotions, but restructuring them through asceticism (abstinence from pleasures of the world) which eventually leads the individual to attain clearer judgment, a strong sense of inner calmness and liberation from suffering/misery. The ultimate goal of stoicism is freeing your life from suffering.