To me, this is pretty closely related to "the U" - election.  If we (humans) get to pick, then the grace is resistible.  If God picks, the He is sovereign and His will be done, always.

On April 6, 1856, Charles Spurgeon gave a sermon on the "Effectual Calling" (Irresistible Grace)

Can I not remember when God told me to come down? One of the first steps I had totake was to go right down from my good works. And oh, what a fall was that! Then I stood upon my own self-sufficiency and Christ said, “Come down! I have pulled you down from your good works and now I will pull you down from yourself-sufficiency.”

Well, I had another fall and I felt sure I had gained the bottom, but Christ said “Come down!” And He made me come down till I fell on some point at which I felt I was not savable. “Down, Sir! come down, yet.” And down I cameuntil I had to let go of every branch of the tree of my hopes in despair.

Then I said, “I can do nothing. I am ruined.” The waters were wrapped round my head and I was shut out from the light of day and thought myself a stranger from the commonwealth of Israel.“Come down lower yet, Sir! You have too much pride to be saved.”

Then I was brought down to see my corruption,my wickedness, my filthiness.

“Come down,” says God, when He means to save. Now, proud Sinners, it is of no use foryou to be proud, to stick yourselves up in the trees—Christ will have you down. Oh, you that dwell with the eagle on the craggy rock, you shall come down from your elevation—you shall fall by grace, or you shall fall with a vengeance one day. He “has cast down the mighty from their seat and has exalted the humble and meek.”

When God "means to save" -

What I know is this...there is nothing - NOTHING - special about me.  I didn't turn to Christ because I'm smarter, or holier, or more spiritual...

It is only by the work of the Spirit that I can claim to trust.

And trust is a challenge sometimes, but I can no more turn away, than I could stop being...the core of who I am.