Strategy Planning and Strategy Execution

Strategy Process
Understanding how strategy works and being able to execute successful strategy are two entirely different things. Moreover, successful execution does not imply that the chosen strategy was the right one. There are many pitfalls along the way between planning strategy and the final result that can determine success and failure.
The most obvious issue is an unforeseen change in the external environment. What is "unforeseen" is open to some interpretation, of course. If Irma disrupts your Florida retail business, was that unforeseen or should you have baked into your plans the fact that hurricanes do tend to hit Florida from time to time? But often, especially with long-run strategy, there is some disruption, either competitive, technological or even a natural disaster, that changes the competitive landscape. If your company does not adapt its strategy, it will surely fail to achieve the objectives, but even if it does adapt, it might yet fail.
The quality of the strategy is a key issue when it comes to strategies that fail. There are a lot of reasons why the strategic planning process can fail to yield a quality strategy. In particular, decision making can break down when you are data deficient, or when the best available data contradicts conventional wisdom. At that point, the decision-maker might make a decision about strategy that some sense is wrong, but those people no longer have the influence needed to make the decision right again (Merchant, 2008).
Similarly, bad data can yield to bad plans. Predictive strategy in particular is garbage in, garbage out, so if the data used to make the strategic decisions is poor, that increases the risk that the strategy will be poor, and thus fail. Misunderstanding the environment or the market will result in strategy focused on the wrong priorities, with resources wasted on things that were never going to succeed (Aileron, 2011).
Furthermore, creating a good strategy is not enough. Several other key elements need to be in place. One is alignment. If the organization is not aligned with the strategy being pursued, the strategy may suffer for lack of appropriate resources, or focus. An example would be a company that defines its strategy around a product launch, and then puts all of its R&D energy into enhancing the existing product. That is a misalignment between resources and strategy that will ultimately lead to that strategy failing (Sull, Homkes & Sull, 2015).
A lack of buy-in from key stakeholders will also undo a strategy. Usually that will occur because of a misalignment, but ultimately even when the structures in place are aligned, there will need to be buy-in from managers who are then charged with setting priorities, motivating their teams and maintaining focus. A strategy is simply less likely to succeed if the managers haven't bought in, because nobody in the organization will be working particularly hard to see that strategy through to success.
There is also the issue of communication. One of the key execution issues is communication. First, everybody within the organization has to not just listen to the strategy, they need to understand it. That alone is important, but there are many opportunities for communication breakdown throughout the execution. If people misunderstand their roles, the objectives that they are seeking to achieve, or any major aspect of the strategy, then their actions may challenge or even undermine that strategy. Sometimes this happens inadvertently.
No company can produce extraordinary performance just because it went through the strategic planning process well. Execution is an entirely different matter from planning, and there are many steps in the execution of a strategy where that strategy can break down, or see its odds of success reduced.

References

Aileron (2011). 10 reasons why strategic plans fail. Forbes. Retrieved September 19, 2017 from https://www.forbes.com/sites/aileron/2011/11/30/10-reasons-why-strategic-plans-fail/#1ee2337186a8

Merchant, N. (2008). 5 reasons why strategy fails. Entrepreneur. Retrieved September 19, 2017 from https://www.entrepreneur.com/article/195354

Sull, D., Homkes, R. & Sull, C. (2015) Why strategy execution unravels – and what to do about it. Harvard Business Review. Retrieved September 19, 2017 from https://hbr.org/2015/03/why-strategy-execution-unravelsand-what-to-do-about-it