the thing is

US /ðə θɪŋ ɪz/
UK /ðə θɪŋ ɪz/
"the thing is" picture
1.

问题是, 关键是

used to introduce a statement that explains the most important aspect of a situation or problem

:
I'd love to help, but the thing is, I'm really busy this week.
我很想帮忙,但问题是,我这周真的很忙。
He said he'd be here, but the thing is, he often forgets.
他说他会来,但问题是,他经常忘记。