成 become

If you SAY you'll get good at kanji, eventually you will become good.

The scissors fell off the cliff and became dangerous spears, piercing the brains of innocent people below. (see also: pennies dropped off Empire State Building become bullets)

completion ★★★☆☆
完 (complete) + 成 (become) = 完成 (completion)

completion (noun) - usually said of a painting, construction of a building, or other physically creative project.

success ★★★☆☆
成 (become) + 功 (success) = 成功 (success)

oh, I see! ★★★☆☆ KUNKUNKANA
成 (become) + 程 (extent) = 成程 (oh, I see!)

"ohhhh, now I see!" (very similar to a hearty 分かった！！　（わかった）, but it also has the nuance of, understanding AND agreeing whole-heartedly)