Looking for a good analogy!

I've recently been finding analogies quite helpful when explaining something to clients. Something I'm explaining on a regular basis is that causing users to stop and pause to think about something can seem quite negligible (sometimes it can just be a half of a second pause), but when confronted with multiple instances of these pauses they can add up and amount to a bad user experience.

Does anyone have a good analogy for this? Any ideas welcome!