You want to change

You don't want to do the old way of doing things. It's ineffective, so you're moving away. To give some examples, you don't want to be poor or bad with money anymore. You don't want to be fat. You don't want to be mistreated at work. You will finally live the life you're meant to if only this "thing" wasn't preventing you etc.

Another example, you would always imagine there would be a defining moment where you change and you don't look back. There's this line and you're a different person after crossing it. A proverbial crossing of the Rubicon. There's no going back. Crossing the Rubicon has rarely worked for me because the thinking and the behaviour is still left behind, which steers me back to the old direction I don't want to go.

Sometimes those parts aren't cemented in even though you have the best intentions or purpose.

The other side is you need it to be big enough to start otherwise you won't start. You're damned if you do and damned if you don't.

Small and just enough behavioural change is where it's at. But there's a gap you need to fill in. Motivation. You won't be able to start with it. You'll just have to start. You'll get the motivation and the feel-good things later.

Or you commit so heavily to the change and burn all bridges so there's no going back. The line becomes a cliff face and you can't go back.

Choose your poison, they both work.