kidding oneself

(idiom) lying to oneself

Example Sentences:

A: I think I’m going to become an Olympic athlete!
B: You are kidding yourself. You’re overweight, lazy, and terrible at sports!

The student was kidding herself when she thought she would complete a four-year program in two years.

From the Blogs:

Emotional Cheating -- Stop Kidding Yourself

Media:

Similar idioms:

1. beside oneself
2. bring up
3. give oneself a pat on the back
4. shoot oneself in the foot
5. knock oneself out