wishful thinking

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Thinking in which what one wishes were the case is believed to be real or likely to become real.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic, psychology The illusion that what one would like is actually true.
• noun idiomatic Decision-making based on self-delusion.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the illusion that what you wish for is actually true