the thing is
US /ðə θɪŋ ɪz/
UK /ðə θɪŋ ɪz/

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.