Abandon the essential and work hard on the small things.

It should be these:

Don't do good deeds because they are small, and don't do evil because they are small. And do it." (Liu Bei's teaching son)

"The accumulation of soil will form a mountain, and the accumulation of water will form a abyss."

"Those who cannot do small things cannot do big things." ——Lomonosov

“If you don’t sweep one house, how can you sweep the world?” ——Xue Qin