It's when you *want* to do something, but the transition from what you are currently doing is effectively stopping you from doing the new thing.
Let's give some examples.
There's always that "last more thing" which really isn't a last more thing and you can easily do it tomorrow, but it's an expression of not being able to transition to another activity.
"Sure, I love to!"
But then, I'd have to prepare and we'd have to find a place to go to and it all feels like too much hassle. As in: I have a hard time stopping what I'm doing (even if it's nothing substantial), and moving on to something else.
I'll probably start by the time dinner should have been served because The Chasm. I generally like cooking, but I need a deadline to be able to jump over the chasm.
Like I said, "boring"/have-to activities are easier to navigate away from, but never "easy" easy. And navigating to them can be even more challenging in a lot of cases.
Don't ask me "What do you want to do?". There's literally a ton of stuff I'd like to do, but all of them are on the other side of The Chasm.