Just because everybody believes this myth doesn't make it true. Ask yourself what elements of today's so called common knowledge you're likely to be chuckling over in five years. Things are running well, let's do the planning when we need it. T. J. Watson, the founder of IBM was fond of saying that he was the most afraid when things were going well. Complacency is more dangerous than any competitor.
Profits are highest in mature markets and products.
The sweetest time is in the Autumn, just before winter hits. It takes time to develop the next big thing that will replace your current cash cows. Strategic planning provides a forum for sorting though the myriad of potential investments and selecting and nurturing your future winners. I was with a company for 15 years that developed a rich and lucrative market. We knew the days were numbered and we would have to replace it eventually.