Honesty is the Best Policy

Moshe already knew about the Golden Calf while he was still on the mountain, so why carry the Luchos all the way down before breaking them? What did he see as he came closer that changed everything? The Sforno points to one detail in the pasuk about what the people were feeling, and it says something about how we perform mitzvos and how we do the things we know we shouldn't. A second answer, built on a Gemara about a sin done more than once, cuts even closer.