erfolgreich
successful
Having achieved the desired goal or a positive result; with success.
Nach langem Training war sie bei dem Wettkampf endlich erfolgreich.
After long training, she was finally successful in the competition.

successful
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successful
Having achieved the desired goal or a positive result; with success.
Nach langem Training war sie bei dem Wettkampf endlich erfolgreich.
After long training, she was finally successful in the competition.

The adjective 'erfolgreich' (successful) is made up of the noun 'der Erfolg' (success) and the suffix '-reich' (-rich, full of). It literally means 'rich in success.'
Sie ist eine sehr erfolgreiche Geschäftsfrau.
She is a very successful businesswoman.
'Erfolgreich' (successful) can be used as an adjective before a noun, as part of the predicate with 'sein' (to be), or as an adverb to describe a verb.
Das war ein erfolgreicher Tag.
That was a successful day.
Common verbs that are combined with 'erfolgreich' (successful/successfully) are 'sein' (to be), 'werden' (to become), 'abschließen' (to complete), 'beenden' (to finish), or 'verlaufen' (to go/proceed).
Das Meeting ist sehr erfolgreich verlaufen.
The meeting went very successfully.
happy / lucky
'glücklich' and 'erfolgreich' can both describe that something turned out well. 'erfolgreich' clearly says that a goal was achieved. It fits well with exams, projects, conversations, or plans. In this context, 'glücklich' can mean that something ultimately went well or favorably, often with some luck. Learners confuse the words because success can make people happy. But 'erfolgreich' describes the result; 'glücklich' describes either a feeling or a particularly good outcome.

Die Klasse bereitet sich gut vor und besteht die Prüfung erfolgreich.
The class prepares well and successfully passes the exam.
Nach einem schwierigen Start nahm die Reise doch noch ein glückliches Ende.
After a difficult start, the trip did have a happy ending after all.