jì / rán / jué / dìng / cān / jiā / bǐ / sài / jiù / yīng / gāi / quán / shǐ / quán / zhōng / de / jiān / chí / xià / qù

既然决定参加比赛，就应该全始全终地坚持下去。

Now that you have decided to enter the competition, you should see it through.