Some people (actually quite a few people I know) seem to have a difficult time grasping the following concept:
When you say "I want to do ___ with you" and ___ is contingent upon you accomplishing a task, you must actually complete the task OR have a decent reason otherwise the only conclusion I can come to is that you don't actually want to do ___ with me".
In other, simpler words:
If you don't keep your end of the bargain, and you have hidden this fact from me, I can only assume you are not interested in the rewards.
now repeat this in front of a mirror every day until you gain sudden enlightenment:
"I will not promise what I am afraid to deliver."
