This is the 8567th most frequent Japanese word.
捨て去る
"To abandon or throw away completely."
捨て去る is used to express the act of decisively letting go or giving up something, in this case, his past.
彼は過去を捨て去る決心をした。
He decided to abandon his past.
捨て去る here conveys the idea of mentally discarding negative emotions, such as anxiety.
不安を捨て去り、新しいことに挑戦しましょう。
Abandon your anxieties and challenge new things.
捨て去る is used to indicate the act of giving up on a plan or idea that didn't go as expected.