You might think:

"I've had the worst day. I deserve this".  OR "I already blew my diet-I might as well keep eating".

You're feeling:

Stressed, frustrated, or maybe even guilty.

You ate a large amount of food that you didn't plan to, which leaves you feeling worse.

CBT helps you question that automatic thought:

"Is food actually helping my stress?"

"Does one slip-up mean that I've failed?"

You might reframe it as:

"Today was not great, but eating won't fix it.  I can take a walk, vent to a friend, or watch something relaxing instead."

Instead of emotional eating, you choose a healthier coping strategy and remind yourself:

"One slip-up doesn't ruin my progress.  I'll draw a line under it and get back on track now."