Giving something everything you have. Everyday, sincere, and with a good backstory.

What a Japanese person actually thinks
Completely everyday and completely sincere. It's what a coach says, what a parent says, what you say about someone who's trying hard. Nobody will find it cool; everybody will find it genuine.

Meaning

Literally: one + life + staking + fate
Actually: Doing something with all your strength. Originally 一所懸命 — 'staking your life on one place', i.e. a samurai defending the single plot of land his family held. The 所 drifted to 生 over centuries.

Scores

Naturalness●●●●●

Extremely common. Both spellings are correct; 一生懸命 is now standard.

Coolness●●●●●

Four solid characters, and the land-defending etymology is a genuinely good thing to be able to explain.

Watch out

Nothing embarrassing lurking in here.

On skin

一生懸命

Orientation: vertical

Mincho, vertical.