an uphill battle字面意思上坡作战，引申为在逆境中求胜；艰难的战斗；一场艰苦的战斗。

【例句】
Finding the one big love has always been an uphill battle.
找到一个让自己深爱人，就好像一场艰难的战斗。

It's an uphill battle but I think we're going to win.
虽然这是一场艰苦的斗争，但我相信我们会取得胜利。