Changing your habits always feels hard initially.
Regardless of whether you're trying to stop smoking or drinking or drugs or over-eating or going to bed too late or being irritable or too angry or impatient. When we're comfortable doing things the way we've always done them, our brain finds it much easier to just keep doing it that way.
The same is true for changing thinking habits.
We have so many thoughts firing through our heads each day that often it's easier for us just to get stuck ruminating on the ones that come our way rather than trying to change which ones we give attention to.
But just like going on a physical diet helps us change our body shape, going on a mental diet helps us change our happiness levels.
Do you need to go on a mental diet?
If you do, the '7 Day Mental Diet' by Emmet Fox is a great place to start.
It won't be easy initially.
But nothing great is.