Seen sideways it becomes a ridge, seen end-on a peak - near, far, high, low, each view is different.
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From Su Shi's 《题西林壁》 (Song dynasty), written on the wall of Xilin Temple on Mount Lu: 横看成岭侧成峰,远近高低各不同。不识庐山真面目,只缘身在此山中。 The poem became a paradigmatic Chinese expression of perspectivism - you can't see the whole mountain when you're on it.
usage
Always cited with 横看成岭侧成峰 as the full couplet. The poem's last two lines 不识庐山真面目,只缘身在此山中 are even more famous - the whole quatrain is one continuous argument.