How do you convince yourself to take action?

I can't motivate myself. I know exactly what I want to do, and why I want to do it, but somehow that isn't enough. I tell myself that I am going to do it, but I never do. It is especially bad the longer I have been putting off the task or activity. I just can't seem to convince myself to do anything no matter how much I want to, so I do nothing all day. How do you convince yourself to do things? How do you overcome the lack of motivation from depression? Any tips?

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