You have a plan and you think about everything that will be required to get the project through. It seems like so much work, so many resources and so much time will be needed. Instead of driving you to action, this analysis leads to inaction. This inaction makes the problem seem insurmountable and thus more daunting. The cycle is vicious!
The solution is simple: Take action. Instead of thinking of the massive goal, think of small steps that will eventually lead to you achieving said goal.
For example, if you want to lose 40 kg, getting everyday and focusing on that enormous task will lead to a feeling of constant failure as you will never achieve said goal on any day. A much better approach is to focus on daily goals that will get you closer and closer to your target.
For example: Today I will eat a healthy breakfast and walk 5000 miles. That's all you need to do. You just need to take that step. Once you are there, the next step will be logical and not seem so high or hard.
Whatever your goal is, take action now no matter how small