Elizabeth said:
勝ち目はない (Katachime wa nai)
As Liz implies, you wouldn't want this as a motto... "I have no chance of winning" (maybe the current NZ rugby league team could use it)
My dictionary has:
"in the face of heavy [or terrible, great] odds" 優勢の敵をものともせず (yuusei no teki o mono to mo sezu)
Literally "defiantly standing against a superior enemy"
"against long [or fearful]odds" 強い相手に対して (tsuyoi aite ni taishite)
Literally "against a strong opponent"
"fight against long odds" 強敵と争う (kyouteki to arasou)
Literally "to fight against a strong enemy"
The first two are "sentence fragments". You could use the first one as a motto but not the second one (grammatically speaking).
You might be better off with something not so "metaphorical" in the original English. Here are some from the Doraemon story "Kurou Miso", translated by me so there may be some mistakes.
"艱難、汝を玉にす" (kannnan nanji o tama ni su)
Literally "Hardship turns you into a jewel" (improves your character)
"我に七難八苦を与えたまえ" (ware ni shichinan hakku o ataetamae)
Literally "Bestow on me the seven hardships and eight sufferings"
"憂きことの尚この上に積もれかし、限りある身の力試さん" (ukikoto no naoko no ue ni tumorekashi kagiri aru mi no chikara tamesan)
This is another kind of "prayer" to Heaven like the one before, literally "Pile your hardships upon me, do not try (in the sense of "test") the strength of weaklings"
"苦労は金を出しても買え" (kurou wa kane o dashite mo kae)
Literally "Undergo hardships even if you have to pay money to suffer them"
These are sayings from back in the old
Samurai days before the "age of hikikomori"... sigh...
You need a native speaker to give you a good motto.