Today's sell-off in Novo Nordisk may be the buying opportunity you've been waiting for.Bad news for Novo Nordisk (NVO -17.34%) Friday was good news for Eli Lilly (LLY 4.92%) and Viking Therapeutics (VKTX 6.33%), its two main rivals in the field of weight loss drugs. This morning, Novo reported headline results from its phase 3 trial of a new weight loss drug, CagriSema, and while objectively not bad, the results were less great than Novo was shooting for.As of 11:05 a.m. ET, Novo Nordisk stock is down a dis ...