Whatever you're trying to do, there's a Day 1.
Be kind to yourself on Day 1.
Do only what is necessary to accomplish Day 1, and nothing else.
If that means not doing something you'd normally be doing, then that's what it means.
Make Day 1 as easy as possible.
And let yourself feel whatever you need to feel on Day 1: angry, annoyed, inconvenienced.
Because by Day 2, you'll have already begun --
You'll be in motion, as opposed to starting from nothing.
Example: reducing caloric intake.
On Day 1, don't worry about exercise. Just have your smaller meal. Even days 2, 3, 4 and 5 -- don't work out. Just walk, and eat your smaller meals.
The recognisable dent these 3-5 days will make will 100% inspire and give you the fuel you need to take on Days 6 and 7, then another week (where you will naturally work out without effort) after that.