Isaiah 26:3 You keep him in perfect peace whose mind is stayed on you, because he trusts in you.

Meanings of words change over time. Dictionaries change due to social use so in order to rightly understand stayed we must look to the original translation. Stayed in this context is most closely related to leaning upon that which is upright and unmoveable.

Proverbs 3:5 Trust in the Lord with all your heart, and do not lean on your own understanding.

We once again find the clear distinction between the mind and the heart.

1 John 4:16 So we have come to know and to believe the love that God has for us. God is love, and whoever abides in love abides in God, and God abides in him.

1 John 3:17 But if anyone has the world’s goods and sees his brother in need, yet closes his heart against him, how does God’s love abide in him?

The mind is the seat of reason, the heart is the seat of God’s love for those who believe by faith. Therefore trusting the Lord is leaning on the love that abides in our hearts rather than reasoning with our minds which are constantly being bombarded by worldly influences.