schwierig
difficult
Not easy to manage, solve, or understand; requires effort or skill.
Das war eine wirklich schwierige Matheaufgabe.
That was a really difficult math problem.

difficult
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difficult
Not easy to manage, solve, or understand; requires effort or skill.
Das war eine wirklich schwierige Matheaufgabe.
That was a really difficult math problem.

The adjective 'schwierig' (difficult) belongs to the word family of 'die Schwierigkeit' (the difficulty; the problem, the obstacle). When something is schwierig, it causes difficulties.
Die größte Schwierigkeit war, alle Termine zu koordinieren.
The greatest difficulty was coordinating all the appointments.
'Schwierig' is very often used in the construction 'es ist schwierig, etwas zu tun' (it is difficult to do something). Here, 'es' introduces the sentence, and the infinitive with 'zu' describes the difficult action.
Es ist schwierig, ohne Vorkenntnisse einen Job zu finden.
It is difficult to find a job without prior knowledge.
If 'schwierig' describes a task, a problem, or a question, it means 'not easy.' If it refers to a person, it means that it is hard to get along with that person.
Die Prüfung war sehr schwierig.
The exam was very difficult.
To describe problematic phases of life or circumstances, 'schwierig' is often combined with nouns such as 'Zeiten' (times), 'Situation' (situation), or 'Lage' (position/situation).
Das Unternehmen befindet sich in einer finanziell schwierigen Lage.
The company is in a financially difficult situation.
simple / just
'einfach' and 'schwierig' are opposites when talking about tasks, questions, or situations. Use 'einfach' when something is easy to understand or do. Use 'schwierig' when something requires effort, time, or a lot of thinking. They can be confused because both words often talk about the same area: how well you can solve or understand something. The practical difference is clear: 'einfach' means little problem; 'schwierig' means a big problem or many problems.

Bei dem Termin ist die Entscheidung schwierig, weil viele Personen betroffen sind.
At the appointment, the decision is difficult because many people are affected.
Die Erklärung am Telefon war heute einfach und gut zu verstehen.
The explanation on the phone today was simple and easy to understand.