the thing is

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

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.
He said he'd be here, but the thing is, he often forgets.