Thomas Aquinas Commentary Lamentations 4:17

"Our eyes do yet fail [in looking] for our vain help: In our watching we have watched for a nation that could not save." — Lamentations 4:17 (ASV)

Here he excludes the possibility of escape, ruling out four potential ways of escape.

1. The help of friends: while we were still standing, we were waiting, expecting help for us in vain, namely, the Egyptians. For Egypt shall help in vain, and to no purpose (Isaiah 30:7).