is to blush unseen 语法成分剖析？

1) Many a flower is born to blush unseen.

2) The trouble began in Laredo. It was the Llano Kids fault, for he

should have confined his habit of manslaughter to Mexicans. But the

Kid was past twenty; and to have only Mexicans to ones credit at

twenty is to blush unseen on the Rio Grande border.

请教老师，以上2句中都出现了is to blush unseen:

is to 是什么使用方法？

unseen是主语补足语=表语吗？

麻烦老师具体剖析一下语法和成分，谢谢！

参考die young