Zuòshì qing bùnéng hǔtóushéwěi, yào shànshǐshànzhōng.
Don't start strong and fizzle out — see things through from beginning to end.
Zhèbù diànshìjù qián jǐ jí hěn jīngcǎi, hòumiàn què hǔtóushéwěi.
The first few episodes of this series were great, but it fizzled out toward the end.
