You Made an Attempt to Engage Your Child and You Were Rebuffed
You approach your child and say, "Let's play together," or, even better, you say, "Let's play whatever you would like." Your child says, "No thanks, Dad. I don't want to play now."
You feel rejected. ("Well, if he doesn't want to play with me, to heck with him.") You feel hurt and self-righteous about not offering again. "I tried," you say to yourself.
But certainly you would agree that, just because you found the time to play with your child at that particular moment, it is unreasonable to assume that your child will necessarily want to interrupt what he may be involved with in order to respond to your unexpected overture. He may also be reluctant to accept your offer for fear of being disappointed once again because your interest will not last very long.
Don't let your ego interfere.
Instead of walking away and shaking your head after your child says, "Not now, Dad," simply respond with "Okay, let's make a specific date for another time. What do you think might be fun? When would you like to do it?"