It used to be viewed as good when one kept his/her "nose to the grindstone". Singular, fixed focus on a task until it was completed as planned was a good thing. This is the approach used in old school project management where meeting the triple constraint (schedule, budget, specs) was THE criterion for success.
But that is not the case anymore so I find myself saying the old baseball mantra instead: "Keep your eye on the ball". This is because the pace of work constantly varies (fastballs, change-ups) and projects are frequently throwing us curveballs (changes in state of the art, strategy alterations, new challenges from competitors, etc.).
And heaven knows we encounter our share of screwballs too.
So while we still need to make thorough plans, we also must be ready to react and adapt. If we prepare for contingencies properly and do keep our eyes on the ball maybe we'll hit one out of the park now and then.
...and don't even get me started about all that requires our attention before we step into the batter's box (game situation, positioning of fielders, signs from our coaches, etc., etc.)
If our noses are to the grindstone we'll miss everything else going on around us, and that's no longer viewed as ok.