I recently completed a challenge called 75 HARD. It was a mental challenge that I needed to help me get through the months of lockdown in Sydney.
It is a mental challenge to complete a list of tasks every day for 75 days straight. Miss one of these on any given day... you go back to the start at Day 1.
Here are the daily tasks:

2x 45 mins workouts of your choice (one must be done outdoors)

Choose a diet and stick with it

Take a progress photo each day

Drink 4L of water each day

No alcohol or cheat meals

Read 10 pages of a non-fiction book
Sounds easy for 1 day. But doing this for 75 days in a row is a challenge.
Here are the lessons I learned from attempting the 75 Hard Challenge:
1. Win the Day
2. 3 Progress Phases
3. Details and Accountability