When I was in college, I was a psychology major. I took many classes on personality theory as well as abnormal psychology. I had to repeat the process during my Master's degree, so one could argue that I am rather well versed in the theory of Psychology in all its forms.
In fact, during one grad class in abnormal psych, one of the students asked for a better, more "real life" explanation of what Borderline Personality Disorder would look like in a patient. The professor was a parent of something like 3 kids. Her explanation? Imagine someone stuck in the terrible two's for EVER. And, when you run into someone who truly has a borderline personality, and you have parented a toddler through the murky waters of the terrible twos, you see the correlation immediately.
Christopher, my beloved blue-eyed infant of yesterday, is that borderline disordered child today.
Case study: Christopher has discovered the endless buckets of Matthew's Thomas tracks. Christopher loves the tracks. (as an aside - he's not so into the trains at this point; just the tracks) He takes them out of the bucket, lovingly, and places them on the floor with care. He turns them over to inspect each one, gazing longingly at them laid out in front of him.
He then tries to put them together, and this is where all hell can break loose. He becomes so maniacly frustrated with the process that he is rendered speechless, and resorts to primal grunting and wailing for help. This is a sound, by the way, that no wall can contain; the entire neighborhood knows of his misfortune.
So what is a mother do to but to see if I can help. I try to show him how to fit the pieces of the track together. 'If you just turn this one a bit...' which is met with more screaming, so I back off... only to have him, 2 seconds later, hand the track out to me with an emphatic HELP.
Wait; didn't I just try to help and you screamed at me?
Yes, mom, I did, but that was 2 seconds ago and NOW I want your help. NOW I SAID WOMAN - you are NOT solving my problem fast enough.