fall behind

• You’ve got to keep up with it. Once you fall behind, it’s hard to catch up.
  遅れずについていかなくちゃ。一度遅れをとったら追い付くのは大変だよ。

fall behind
後れを取る、脱落する、落後する、〔学校などで〕落ちこぼれる
・She missed three weeks of class and fell behind in the course. 彼女は授業を3週間休んでしまったので、勉強が遅れてしまった。
・Otherwise, they fall behind other contries. そうしなければ他国に後れを取る。
・I don’t want to fall behind my class. 勉強が遅れるのはいやだ。
・I fell behind in my schoolwork. 勉強が遅れた。

チャット爺に訊いてみました。

Sure, here are five sentences using the phrase “fall behind”:

• He was worried about missing classes and falling behind the rest of his classmates.
• The project started well, but due to unforeseen issues, we began to fall behind schedule.
• Without consistent practice, it’s easy to fall behind in your language learning goals.
• The team fell behind in the first half of the game but made an incredible comeback after halftime.
• She’s been feeling overwhelmed at work and fears she might fall behind on her assignments.