C2 不明白，不理解
used when you do not accept something
I fail to see why you can't work on a Saturday. 我不懂为什么你星期六不能工作。
I fail to see the appeal of these highly expensive products.
I fail to see why it's necessary to cut down these beautiful trees.
What I fail to understand is why her actions upset you so much.
The matter seems quite simple to me and I fail to understand why it is proving so hard to resolve.
See also: fail verb (NOT DO)