Take your eye off the ball
Definition 1 of 1
Pro Tip 1/3Sports Origin
The phrase originates from sports and keeping focused on the ball. 
An outfielder can't afford to take their eye off the ball.
Pro Tip 2/3Figurative Use
It's often used metaphorically to discuss focus in non-sport situations. 
You took your eye off the ball when you ignored the client's concerns.
Pro Tip 3/3Negative Outcome
Losing focus can lead to mistakes or negative consequences. 
The project failed because the team took their eye off the ball.