wieso
why
Used as a question word to ask about the reason or cause of something. Synonymous with 'warum' (why).
Wieso hast du mich nicht angerufen?
Why didn't you call me?

why
Loading your saved state.
why
Used as a question word to ask about the reason or cause of something. Synonymous with 'warum' (why).
Wieso hast du mich nicht angerufen?
Why didn't you call me?

'Wieso' is a compound of the words 'wie' (how) and 'so' (so). You can therefore think of it as the question 'In what way so?' or 'How did it come to be like this?', which explains the meaning 'warum' (why).
Wieso ist der Himmel blau?
Why is the sky blue?
Word order depends on the function. In a direct question with 'wieso' (why), the verb is in position 2. In a subordinate clause introduced by 'wieso', the verb comes at the end.
Wieso kommst du zu spät?
Why are you late?
Compared with other question words for the reason, 'wieso' often expresses particular surprise or even doubt on the part of the speaker. You use it when you really did not expect something.
Wieso denn das? Ich dachte, wir wären uns einig.
Why that? I thought we agreed.
why
'warum' and 'wieso' are both used to ask about a reason or cause. In many direct questions, you can use both words in the same way: 'Warum kommst du spät?' and 'Wieso kommst du spät?' mean almost the same thing. 'warum' is very neutral and fits in almost all situations. In conversation, 'wieso' often sounds a little more spontaneous or personal, and sometimes a bit surprised. Both can also be used in indirect questions when you want to know for what reason something happens.

Die Mitarbeiterin hat gefragt, wieso der Termin verschoben wurde.
The employee asked why the appointment had been postponed.
Warum seid ihr nach der Arbeit nicht zum Treffen gekommen?
Why didn't you come to the meeting after work?