A bridge leading to nowhere is a waste of time, no one should climb such bridge. The bridge might not be a literal bridge but it can be a destination or a dream leading to nowhere, such a waste of time.
This is an analogy that fits the scenerio well. A person going towards a direction but cannot see way ahead of him, he hopes the road leads somewhere fruitful so he keeps going. If he knew the road would lead to nowhere, he would not tread that path. This is the case for some of us, we tread the path that leads to nowhere, hoping we would find our way somewhere in-between. It is better you know where you are going, than to gamble away your time in treading an unknown path.
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