wantstoleave: I just want to clarify this, not because you're technically wrong, but because JWs often take that 2% way too literally, and they argue that this is a proof that man was not created to live such a short life. In short: technically speaking you do use 100% of the brain. If you wouldn't, then you shouldn't mind me taking out 90% of your brain right?
However the brain does have the capability to do more. Here's an example (saw this on an other webpage): think of a stereo system. When you're listening to music, are you using the whole system 100%? However you have a knob to turn the volume up and down. When the volume is at 2% are you using 2% of the stereo? No, you're still using it fully.
There is absolutely nothing stopping you from using more of your brain right now! There are no blocked brain cells, that are waiting for God to release them. Technically with hard learning, and perseverence you can use much more than you are using now, and this was proved true by many who just wanted to best themselves. Our short lifespan is sort of a limiting factor, we start to decay way too early, but the average life expectancy is continually increasing, and some say the average intelligence is increasing too.
So I just proved that indeed our lives are too short to use our brains But long life is not equal to fully using brains, because it only gives you the time to best yourself, it won't come automatically. However one could argue that such mechanisms are present at the animals too, and they are not expected to live eternally even in Paradise.
On the other hand you have a point there, as someone said: "If our brain were so simple that we could understand it, we would be so simple that we couldn't"