One way to hold tortuous is a line drawn by someone who keeps changing their mind: left, then right, then left again, never long enough in one direction for you to see where it is going. Nothing about that line is steep and nothing about it is far. The cost is all in the turning. You cannot see ahead, you cannot keep your speed, and the distance on the map turns out to mean nothing. Once you have the line, you can lay it over a mountain road or over a page of writing, and the complaint is the same either way: this could have gone straight, and it did not.
From the word’s history
The word comes through Old French from Latin tortuosus, built on tortus, a twisting or winding. The modern uses have not moved away from that: whether it is a road or an argument, tortuous still names turning.
這個字經過古法文，來自拉丁文 tortuōsus，而它的底是 tortus——扭、繞。今天的用法完全沒有離開那個字根：不管講的是一條路還是一段論證，tortuous 說的都還是「一直轉」。
Wiktionary, "tortuous"
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