"Running Light Without Overbyte"

Motto of the original "Dr. Dobb's Journal of Computer Calisthenics and Orthodontia"

Memory is a finite resource on these tiny processors and some applications are just plain too big for an Arduino. But most code has some room for optimization. So if your program is just a little overweight, with a little diet and exercise, you can probably shed enough bytes to make it fit into that Uno again.