When we are weak we are strong according to God. At first is makes no sense when we read such words in scripture. But scripture always proves itself right in the end if we dwell on it long enough.
You see when we feel strong we are quite foolish. We are frail if we know it or not. The strongest athlete and the richest man in the world are vulnerable and frail. Often we see "great men" express hubris of their invincibility, but we are frail. Maybe today we are strong but in the end we all succumb to death.
When we admit our weakness we admit the truth. When we feel we are strong we are in delusion. It is God who gives and takes strength. God who gives and takes success.
We often feel that we can succeed apart from God and it may appear for a time to be so although it is not true ultimately or in the short term. Admitting weakness is accepting the truth that it is God behind all good things.
When we feel strong we are in delusion. When we feel weak and turn to God we admit the truth and in that moment we understand reality correctly. God is the strength behind all things and when we admit the truth we understand reality as it is.