I'll think about it...
How many times have you uttered the phrase "I'll have a think about it". The question I want to ask is... did you? Really? Honestly?
Did you actually go away and think constructively about whatever the issue was? I suspect not. That's because it's very hard to think something through, with only yourself to bounce ideas around. I suspect what is really useful about that statement is the opportunity to take some time out.
So... next time you find yourself saying you'll "think about it", catch yourself, agree you need a break, and arrange a time to discuss the matter again.