Where your strength ends
Start where it matters most: God's strength begins where yours runs out. There is a point in every hard stretch when your own resolve is gone and there is nothing left to grit through. That is not the failure it feels like, it is the doorway. God gives power to the faint, not to the people who have it handled. So stop trying to manufacture more grit. Tell Him plainly that you do not have what this requires, and ask for His strength in place of yours. That is not giving up, it is how you make it through.
He giveth power to the faint; and to him that hath no might he increaseth strength.
Isaiah 40:29 · ASVIsaiah speaks to a tired, exiled people and says God gives power to the faint and strength to those with no might left. His help is aimed precisely at the empty-handed, not the self-sufficient.
My grace is sufficient for thee: for my power is made perfect in weakness.
2 Corinthians 12:9 · ASVPaul begged God to remove his weakness, and God answered that His grace was enough and His power is perfected in weakness. The point is that human weakness is the setting where God's power is most clearly displayed.
My flesh and my heart faileth; but God is the strength of my heart and my portion for ever.
Psalm 73:26 · ASVAsaph admits his body and resolve fail, then names God as the strength of his heart. When human resources give out, God Himself is named as the strength that remains.
I can do all things in him that strengtheneth me.
Philippians 4:13 · ASVPaul writes this from prison, content in any circumstance, crediting Christ who strengthens him. The doing is real, but the power for it comes from Christ, not from his own grit.