Yeah, doesn't really work for me either - even when I knew that I'd be much happier after completing the task (e.g., cleaning my room), but nope. I'd just sit there, staring at what I had to do, unable to do it. Then I started reading about ADHD and executive dysfunction and it started to explain a lot - at least for me, the task has to be relatively enjoyable in and of itself for me to do it. The prospect of a reward afterwards doesn't change that and doesn't motivate me to do it. Now I take medication and it's made a noticeable difference to how difficult it is to do unenjoyable tasks.