couldn't

[navi tasan]

Is this sentence correct:
1-Yesterday, I was sure that our team couldn't lose.

Meaning: I was sure that it was impossible for our team to lose.

[Tdol]

Yep, but they probably let you down.

[navi tasan]

I didn't stay on to see the end of the match. I had to get on a computer and type in my questions!!

Another question:
Are these correct:

1-I knew that our team might lose.
2-I knew that our team could lose.

(This can/could business gets me every time. I am trying to put some order in my brain!! I think the affirmative and the negative don't work the same way.)

[Tdol]

They're both correct.

[navi tasan]

Thanks Tdol.
I couldn't be more grateful.

[Tdol]