The antonyms for the word "un-decided" are clear, certain, and resolved. When someone is clear about their decision, they have made up their mind and are resolute in their choice. When someone is certain about their decision, there is no doubt, hesitation or uncertainty in their mind. Finally, when someone is resolved, they have made a decision determined to achieve it.
Being decisive is crucial in personal and professional life, as it shows that one has the ability to make choices and stick to them. An inability to be decisive can lead to missed opportunities or wasted time. Therefore, it is essential to develop the ability to make clear, certain, and resolved decisions to achieve success in life.