The Flash, Season 4

Leo:
Do you know how many rebels we lost over the years, Barry, trying to defeat those Nazi bastards?

Barry:
Countless, I'm sure.

Leo:
Not countless. Counted. Eighteen thousand, three hundred twenty-two. Three thousand, six hundred and seventy-nine were under my watch. And I felt the weight of each of their deaths. I still do, some years after they died.

Barry:
Leo, look, I–

Leo:
The thing I realized is that to continue to lead, to be clear-headed, I had to grieve those men and women I lost. So I did. Each and every one... Look, Barry, you want me to help you move a meta-human nuclear bomb that some genius with nearly every meta-power on this board is after. I will do what I can, as long as your head is on straight. Because if I die before Ray and I get married, Ray will kill me.