A word like circumlocution looks hard until you split it: circum means around, locut means speak, so it is talking around a point. The same move decodes dozens of words from one root. From spec, look at, you get circumspect, looking around before acting, and perspicacious, seeing through things. From Greek chronos, time, you get anachronism, something out of its time, and synchronous, happening at the same time.
The misconception is that decoding gives you the meaning outright. It gives you a strong guess, and the sentence confirms it. Some words have drifted far from their parts. Egregious comes from e "out" plus grex "flock," standing out from the herd; it once meant distinguished and now nearly always means outstandingly bad. Invidious shares a root with videre "see," but it means likely to cause resentment, from invidia, envy.
Watch for roots hiding inside changed spellings. Capere, take, appears as cap, cip and cept: capacious, incipient, intercept. Greek roots also run in pairs that are easy to confuse. Hyper means over and hypo means under. A Greek mis- means hating, as in misanthrope, while the English prefix mis- means wrongly, as in misjudge.
Rule: split the word, translate the parts, then test that meaning in the sentence before you trust it.