Tā tài jíyúqiúchéng, jiéguǒ fǎn'ér dānwù le xiàngmù.
He was too eager for quick results, and it ended up delaying the project.
Tips
usage
Usually a gentle reprimand or self-admonition. Natural companion phrases: 欲速则不达 ('haste makes waste'), 循序渐进 ('step by step'). Opposite: 循序渐进.
grammar
于 is the classical preposition 'in/at/for,' making the structure 急[于求成] — 'anxious [for] achieving success.' 于 here is never optional; 急求成 isn't idiomatic.
