Have you ever decided to get to work on something and then decided it would be too hard, take too long or be or too upsetting? Sometimes this happens because you're tired, hungry, frustrated or over-caffeinated but sometimes it's because you have a very bad story in your head about what you have to do. If this happens to you, try quantifying, not qualifying. Turn it into a simpler task by focusing on the simple mechanics of it and taking away the story you're telling in your head.
First, ask yourself, "What's so BAD about this?" What's the drama about?! Have you ever wanted to ask a five year old WHY ON EARTH she's sobbing on the floor of the grocery store?! (I have...) If it helps, see yourself as that five your old and ask, "Seriously! What's the drama?!" (But try to actually answer instead of sobbing uncontrollably or throwing your shoes at the ceiling.)
Here's an example. I had a client who hated to wash dishes. Every time she looked at her dirty dishes she felt overwhelmed and frustrated. When she asked herself, "What's the drama here?" she realized the dishes reminded her of all the ways she felt like she was a terrible, total, unredeemable failure of a housekeeper, completely incapable of accomplishing anything domestic. Ever. She realized it wasn't the dishes, it was the shame she had around housekeeping that stopped her. The shame was pretty big.
Second, ask yourself, "If I broke this down into simple minutes/items/mechanics how long/what would it take?" Break it down into anything quantifiable, unemotional. This works especially well for small tasks like dishwashing: "Three bowls, four mugs, three forks, ten spoons, a whisk and a frying pan." It works for bigger tasks, too, like a presentation, but it's about making the steps as small and simple as possible so you can get started, like, "Turn on the computer, open a word document, take out notes from meeting about presentation, read notes, list topics..." I could go on, but you get the point.
When most people do this, they feel better because tasks are more manageable. The client who hated washing dishes found herself saying, "Get over this! It'll take eight minutes!" She timed it, and yeah, it was eight. Eight minutes of work equalled a small course correction with significant long term impact on her attitude about housekeeping. Since then she's gotten curious about how long other things take. Mowing the lawn: 22 minutes, putting in laundry: five minutes, and the list goes on. All of that is so much more manageable. Take away the story. It's so much easier to do things when they're just ... things.