Your brain loves patterns and routines. And so, when you make a difficult task a part of your regular schedule, it stops feeling too overwhelming. Instead of waiting for motivation, train your brain to complete difficult tasks within a fixed time. This will make these tasks less boring and intimidating.
For instance, if you struggle with writing reports, dedicate the first 30 minutes of your workday to it. Over time, it will become a habit to finish the most difficult task first and it will also make you feel accompalished. You can also pair doing difficult tasks with pleasant activity— like listening to music which can help create positive reinforcement. Eventually, your brain will see it as just another part of your daily tasks, thus reducing resistance and making you like it.