I ran a marathon last week. It was so long and I was so tired. I didn't really feel like there was a light at the end of the tunnel until I saw the finish line. 

我上周参加了马拉松赛跑。路程太长了，我非常地累，直到看到终点线，我才感觉有一线曙光！

【关键俚语】

light at the end of the tunnel 

英：a pleasant situation in the future which gives you a lot of hope and optimism

中：曙光乍现