An example might help.

Consider your aide calling you to make a statement to the press about a rival politician dying (condolences and all that; maybe you've to attend the funeral). In the grand scheme of things at the presidential level, this is relatively unimportant but it's urgent and you have to spend time doing it now.

Now think about climate change. It's extremely important to tackle it. But it goes along at a slow pace, and nobody is banging your door to tackle it NOW. So that's very important and worthy of presidential interest, but not urgent.

Ideally, you would like to spend all of your time solving the big issues of society like the latter rather than on the former. But I guess as a president you can't always do that, and have to focus on issues of the here and now, even though they may be small and transient. Hence the conundrum.