Another version of this is called Persistent Starting, and it works for all kinds of things. You give yourself a small milestone that is only a fraction of the total task, and allow yourself to stop after hitting that milestone.

Don’t want to wash all the piled-up dishes in the sink? Just wash two cups. After those two cups, you can stop. But chances are good that you’ll go “eh, my hands are already wet and soapy” and do a lot more than the two cups you initially set out to do.

Don’t want to clean the bathroom? Just sanitize the toilet bowl. Chances are good that you’ll go “eh, I already have the cleaning supplies” and clean a lot more.

Don’t want to mow the lawn? Just do the side yard. The front and back can wait until tomorrow. But chances are good that you’ll go “eh, I’m already dusty and sweaty, and the mower is already gassed up and ready to go. I might as well go ahead and mow the rest too.”

Persistent starting only really works long term if you follow two major rules:

1. The initial milestone shouldn’t be daunting. The biggest challenge is typically overcoming your inertia, so your goal is to minimize the amount of inertia you need to overcome. The important point is that you allow yourself a clear and direct end goal before you even start the task. Give yourself a light at the end of the tunnel, and make the tunnel reasonably short.
2. Don’t feel bad about calling it quits once you hit that milestone. Sometimes, you legitimately won’t have the time or the energy to finish all the dishes. And that’s okay, because you only set out to wash two cups. If you don’t want to continue after hitting your initial milestone, you don’t have to. Give yourself the grace to stop after you’ve reached the initial milestone you set for yourself. Because now there are two fewer cups in the sink than when you started. You can always come back and wash two more later when you have more time and/or energy.

If you always use Persistent Starting to try to tackle the entire task, then you haven’t actually followed rule 1. You’re just trying to lie to yourself in the hopes that it will make finishing the task easier. But finishing the entire task isn’t the goal. The goal is starting the task. If you know you’re lying to yourself and intend to finish the entire task, it won’t actually make starting any easier. So be sure to give yourself permission to stop after hitting that milestone, and only choose to continue if you’re in the “might as well finish it” mood.

Also, if you're still stuck in bed unable to do 20 minutes, do NOT beat yourself up. Take care of yourself and aim for 10 minutes tomorrow.

Even better: if a task takes less than 3 minutes to perform, just stop what you're doing and do it.

It's such a great way to get things done, because eventually you will train your brain into thinking of major projects as a series of bite-sized tasks.

More often than not I blow through the amount of time I tell myself I'm going to spend. One of the few examples where lying to myself produces a positive result, and keeps working. even though, by now, I know I'm lying to myself.