People find their greatest enjoyment when they're fully absorbed in a mindful challenge, known as "flow".
How to get into flow:
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The most important determinant of whether you'll achieve a goal or stay with a new habit is not self-discipline, nor rewards, nor willpower, nor motivation. It is focus.
Having multiple goals spreads out your focus and makes it less likely that you'll complete any of them. Maintain your attention on one goal at a time.
Be aware of your negative thoughts and replace them with positive thoughts. For example, instead of quitting your exercise routine, think about how great you feel.
Focus on the good parts of your life. Be thankful for what you have.
If seeing your calendar all packed causes you extra stress, fill your calendar once a week.
This regular review gives you more flexibility but still lets you meet deadlines and stay on top of longer-term projects.