God's strength is made perfect in our weakness‏

Isaiah 40:29-30
He giveth power to the faint; and to them that have no might he increaseth strength. Even the youths shall faint and be weary, and the young men shall utterly fall:

The opening scripture reveals that God is willing to give power to the faint and to those who have no might.

We all may have our own power that has made us strong and mighty. However, at the moment we feel weary and faint, then we realize the existing power in us is not sufficient to keep us strong anymore.

It is at this moment, that we seek God for the extra power that should be added to the existing power (our own power) in us in order to keep us strong without being weary and faint.

But the Lord is not willing to provide the extra power that is needed to be added to our own power, which has been existing in us from the beginning. Instead, God wants us to lose even the power left in us in order that we become fully exhausted.

It is at this moment that God is willing to give us His power which would never be insufficient to keep us strong for the rest of our journey. That is why God says in 2 Corinthians 12:9 that God's power (strength) becomes full and complete only in our weakness.
2 Cor 12:9 (KJV)
...for my strength is made perfect in weakness...

Do you know how God takes away our own power, which is left in us at the moment we come to him for the extra power we need?

Yes, God does this during the time we wait upon Him for the extra power. In other words, when we wait upon God patiently, we are going to lose even the power left in us so that we become the faint.  Becoming the faint and weak by waiting upon God is the beginning of receiving the full power (this time, we feel 100% of the power is from the Lord) from God.
Isaiah 40:31
But they that wait upon the Lord shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint.

This is God's style of giving us power in order to make us strong. God adopts this style lest we become proud about our own power at any moment and fail to give the Glory to God, which He deserves all the time.

Yes, God knows our heart better than we do. God knows our thoughts at the deeper places in our heart, which even we do not know until they come out. Yes, God does not want to bring the disaster that He had to bring upon king Nebuchadnezzar at the moment he was proud of his own power.
Daniel 4:30-31
The king spake, and said, Is not this great Babylon, that I have built for the house of the kingdom by the might of my power, and for the honour of my majesty? While the word was in the king's mouth, there fell a voice from heaven, saying, O king Nebuchadnezzar, to thee it is spoken; The kingdom is departed from thee.

So, if we get fainted by waiting upon the Lord for the answers to our prayers, we have to realize that we have reached the point where we are going to receive the full power from God to solve all our problems. But unfortunately, this is the point for many Christians to flee away from the presence of God by losing the blessing which God is just about to shower upon them.