Life can be exciting, but falling into a boring routine is way too easy. No matter how important or relevant or exciting a project you have to do is, it can get you bored.
We frequently put a lot of hours in the same projects [maybe because we are told so by our bosses, or just because we want to] and, at some point, we get tired of doing the same thing over and over.
When we decide to create, we commit — or oblige — ourselves to create.
The commitment to perform a long task will, eventually, add a sense of obligation to your activity, removing all fun from it. But I believe you have a choice.
Splitting a project [or a given task] in smaller chunks can help. This way, you can jump from one task to another when you get tired — your brain considers each of those parts as different projects, as different things.
It is like leaving aside a whole project for a while, working on something new, and then coming back to it — something similar to what happens in our mind when we procrastiwork.
Framed this way, getting bored of a given piece of work is an option. While it requires some effort, boredom can [and should] be avoided. If you feel like getting bored is not an option, you may have to consider doing something else. Find stuff that doesn’t get you bored. Go somewhere else.