A vision should be attainable subject to current times and its ability to adapt to changing times.
The best vision is insight; the most-wanted vision is foresight; the business vision is to zoom in the future of business and set the strategy to get there:
Vision should have a direction which sets in clarity: Setting a vision that isn't high enough doesn't challenge the organization to excel. But establishing a vision that is based on unrealistic expectations will either discount the value of even creating the vision or disenfranchise stakeholders. The vision should be attainable; however, the vision shouldn't be a fixed target. It should be stable enough to make it worthwhile to make a concerted effort to attain it and dynamic enough to be able to react to any change in business direction or context. An attainable vision is necessarily not setting precedence to constraints. A vision should be attainable subject to current times and its ability to adapt to changing times. If you set a vision that is completely unrealistic, it is bad for morale and becomes a negative motivator. When people see a vision as attainable they will put in the effort to get there. If it is not attainable the attitude can easily shift to one of why bother trying.
A clear vision is circular than tunnel; multi-dimensional than single lenses; colorful than black and white: It should be vivid enough to tell the story and positive enough to overcome barriers; it touches the heart and mind to drive the actions. An attainable vision is mission possible: A vision is the noun. A mission is a verb. The vision is the picture. The mission is the yellow brick road that leads you to the vision. It's what you have to do to get there. A mission is what you strive to do every day; vision is what you see your company becoming if you stay true to your mission.
An attainable vision takes a solid strategy: Vision without strategy is 'day-dreaming,’ while strategy without vision is blinded. The strategy makes a vision happen. Strategy with guiding is a complex set of related statements used to make choices, motivate the creation of projects, and fulfill the vision.
A vision is where you want to go; a goal is something that pushes in the direction of the vision. Like all things in business, your goals (whatever form they take) must be achievable but cannot be too easy. You would probably gauge whether an initiative or a goal is attainable or not. Vision is much more philosophical and abstract to be deemed attainable or not.