Agency and Client, Strategy and Execution

Back in the agency days, we kept talking about strategies, strategies and strategies. But now on the client side, all of a sudden, we just execute ideas and move really quickly. How to get the balance between strategies and execution? Do we need to have a thorough strategy planned out for every single idea we have? Do we have to have a solid purpose and objective before we execute something? Or we just think of the solutions along the way. Pros and Cons?

Going to explore this further.