決して + Negative-Form-(VERB/ADJ/NOUN) as “by no means (VERB/ADJ/NOUN)”
This grammar pattern is used to express a strong negation of an idea and is commonly translated to “by no means, not in the least, never, etc.” This grammar pattern can be used with verbs, adjectives, as well as nouns, so long as they are in the Negative-Form, whether that be plain or polite form.
Ano class wa kesshite yasashikunai. Toru tsumori nara sugu ni kyoukasho o yomihajimeta hou ga iiyo.
(That class is by no means easy. If you’re really thinking about taking it, it’d be best to start reading up on the textbook immediately.)
Kare wa chuujitsu na hito desukara kesshite tomodachi o uragirimasen.
(He is a loyal person, so there’s no way he’d ever betray his friends.)
Anata wa kesshite hitori jyanai.
(You’re never alone.)