When you spend hours writing it becomes natural. He had a gift. He knew how to express his emotions through rhyme...I've done the same shyt burning blunts with dudes in my studio kicking it for an hr, then just look at them and tell them I'm ready to jump on the beat. A 16 isn't hard to come up with once you've got a direction and the the first 4 bars. I'm sure if Pac had a phone like today's gen, he'd be even quicker with it. Writing little 4 bars here and while dropping a deuce or just cruising and shyt.