Think of assert as standing a post upright: you put your claim, or your position, out where everyone can see it. Re- means doing that a second time. So the picture behind reassert can be seen as a post that was already standing, then leaned over or got pushed — and now someone walks up and sets it straight again. Every use carries the same two conditions: it was there before, and there was a weak stretch in between. The second time is usually firmer than the first.
assert 可以想成「把一根柱子立起來」：把自己的主張或位置明確地擺到檯面上，讓大家都看得到。re- 是「再一次」。所以 reassert 的畫面可以想成：那根柱子本來立著，中間歪了、鬆了，或是被人推了一下，現在有人走過去把它重新扶正。這個字的每一種用法都帶著同樣兩個條件：之前就有過，而且中間有一段變弱的時間。也因為這樣，第二次立起來，通常會比第一次更用力。差別只在立的是什麼：有時候是一句話，有時候是一個人的位置，有時候是一股自己會站回來的力量。
From the word’s history
From re- + assert. The prefix supplies the 'again' and the whole meaning of the word depends on it: without a first time, reassert does not fit.
依據來源記載，這個字就是 re- 加上 assert 組成的。前綴 re- 提供了「再一次」，而這個字的意思整個靠它撐著：如果沒有第一次，reassert 就用不上。
Wiktionary, "reassert"
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