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I think that the most important concept in GTD is next action. It is also the easiest, simplest of ideas to implement. If I want to achieve something, what is the next thing, the next action?
Not all the actions. Not thinking how difficult things are because there are so many steps and obstacles. Just next.
Next Action
The ‘classic’ approach to project planning is to plan all necessary actions, at the beginning of a project. How to account, therefore, for the unplanned spontaneous things that come up during execution?

Next actions enable people to focus more clearly on a project or a challenge without having to think about all the other actions. Get it done and move on.
The planned sequence of actions is useful to understand the path from the beginning to achieving the objective, even if just milestones, to understand whether the project is feasible.
Overplanning
The project planning exercise can be pushed beyond its limits. If a project plan goes into too much detail, then it may need to be updated extremely regularly without much added value.
Planning provides structure, but over-planning removes spontaneity and the creative spark from the individuals doing the job.

GTD allays frustration
Managing frustration means coming to terms with the fact that you cannot do everything today, tomorrow or even this year. Managing frustration, helps to alleviate it.
Doing things helps you understand that you can get some things done, if not all. This makes it important to ensure that the ten things on your to-do list are the most important (and most urgent).
Manage the everyday first
David Allen says that it is better to manage the everyday first then to build into major goals because otherwise major goals are just more things we are not achieving.
Goals or action
The alternative is to focus on goals. But the danger is that far away goals may seem intangible. Actions are doable and take you forward. The experience of doing might help you to confirm or modify your goals.
If we get our world under control, we can then move on to loftier objectives with the trust / hope that we can achieve them …
Although it is good to have goals, Clayton Christiansen essentially says that tasks stem from the higher purpose. Purpose inspires people when they are undecided in what to do next.
Tasks should be doable
The key is writing it down.
Distinguish between goals (desired outcomes) and (next) actions. So if the goal is to ‘get into college’, the next action might be ‘complete the application form’ or even ‘download the application form’. Your brain will understand this better and be able to take action, leading to satisfaction and motivation to continue.
Instead of ‘solve the technical problem on my PC’, write ‘search for information about accessing network drives’.
You need to invest a proportion of your time defining what needs to be done before doing it. Rather like SMART objectives, if you cannot express the requirement, it is undoable.
The 5 GTD horizons
David Allen talks about 5 horizons, or areas of focus stretching out from today’s activities through to the furthest visible horizon. Current activities are within the context of a goal.

Actions and next actions imply a future horizon. When discouraged, it may be useful to remind oneself why you are doing an action today. You might be more motivated if you can recall that it is to meet a future objective.
Mind Like Water
David Allen says that mind like water is a state of calm is what people feel when they learn martial arts (which one?) – meditation as much as strength.
This is the calm feeling of knowing that you are taking action to manage your world. Instead of stressing about the future, you know that all you have to do (if you have reviewed your trusted system) is your established next actions.
Weekly Review
David Allen says that the weekly review is an essential component of GTD. I have found this to be the case. I operate a weekly review which, specific to my business, looks at key quantitative and qualitative indicators. It is an opportunity to reflect on the week and plan next actions.

GTD Tools – The Trusted System
The solution is Trello: listing all the things to do, then sorting them so that you know which is the most important and therefore next action. And then after that, sorting them again and prioritize.