R.D.
OMG, my middle child used to say this, broke my heart, but also made me want to bang my head against the wall.
If she said 'I can't... reach the cereal'... did you try? If not, she had to try, if she did try and still couldn't reach, I'd ask her why not. She'd tell me she's too short. I'd remind her that I use a step stool for the stuff I can't reach, then watch the lightbulb go off in her head... lo and behold, she CAN.
I got her problem solving on her own.. it took a lot of guidance and patience on my end, but it made the 'I can't' go away!! Point you're trying to make: YOU CAN!!