When you're deep in, it may feel like you have no time to pause. No time to take a break, there's too much to get done. Perhaps no time to stop and think about how you're working. No time to step back and improve your processes or work on your tools. Maybe even no time to look after yourself, to recharge, to reflect, to take a walk.
As the metaphor goes, you may feel you have no time to stop and sharpen the saw. Until you do it, and then you may realise you have no time to not stop and sharpen the saw.
Sharpen the saw is habit 7 of Steven Covey's classic The 7 Habits of Highly Effective People