If you can't express the idea in text and text alone, then you haven't broken it down properly.
...and at the planning stage, you are still trying to break down the problem. The core concept behind team thinking is that individually, we often fail to analyse the situation completely, and input from others can show holes in our reasoning and things we've failed to properly consider. The whole, hopefully, is greater than the sum of its parts.
I'm coding alone at the moment, and because I have no-one to bounce ideas off, I frequently find myself heading into dead-ends because the problem domain I'm dealing with is very large, and as there's no-one to discuss things with, I need to prototype to find my mistakes. Then I have to go back and rewrite.