Let's say, for argument's sake, that you're a 15-year-old kid just getting into BMX. A little late, but these things happen. And let's also say that you have seemingly endless resources (let's call them "mom and dad"). So you build up the perfect bike—picking it out piece-by-piece, with "ultralight" this and "XLT" that. No pegs, no brakes, no problem! "Mom, can you strip my Pivotal?"
Yet when you finally get it together and get out into the sun, something still doesn't seem right. It's not that you've hardly ever ridden a BMX bike before and need to build up more strength by riding every day. No, that can't be it. There must be something wrong with the bike. It's still too heavy!
But what else is there? You've already got plastic pedals and plastic barends, a two-inch long slammed seatpost and a stripped and trimmed seat, Kevlar-beaded tires, and enough race parts to get sponsored by the NAACP. Your frame was designed by NASCAR engineers, and your fork was designed by—well, someone who knew what they were doing, hopefully. You've got hollow bolts and ti bolts, ti axle nuts and a hollow-pin, hollow-plate chain. Your gearing is so small that said chain hits your chainstay on the top AND bottom. What else is there?
Here's where the hint comes into play, oh seeker of the unbearable lightness of BMXing. Look at yourself in a mirror (or convenient store window) while sitting on your bike. Do your arms look like this?
If so, maybe start with that four inches of extra metal on the end of your bars.