The antonyms for the phrase "in dither" could be several, including calm, relaxed, steady, peaceful, collected, composed, and unruffled. When someone is not in dither, they are often able to focus on their tasks with a clear mind and a positive attitude. They can tackle their responsibilities with ease, without feeling anxious or stressed. In contrast, being in dither can make simple tasks seem overwhelming, and cloud one's judgment. Learning to stay calm and composed, even in the face of a challenge, is an important life skill that we can all benefit from.