Not many modern day Christians face imprisonment for their attempts to live a Christian life and to announce that they are doing so. But, imprisonment isn't the only cost. We may find ourselves slipping in faithfulness just because of our concern to maintain our own comfort or security.
We might say "Get over yourself."
But not totally over. The letter promises that the short-term sacrifices are, in fact, short term. "If we have died with him, we will also live with him. And if we endure, we will also reign with him."
The letter follows these reassurances with a caution, "If we deny him, he will also deny us."
Yet even that caution is modified with the next assurance, "If we are faithless, he remains faithful."
Although I might prefer just to hold on to that assurance, I am going to offer the explanation made by Allen & Williamson in their Preaching the Letters:
....Affirming or denying Jesus seems to be a quid pro quo--God will treat us precisely as we deserve. But verse 13 counters with "If we are faithless, he remains faithful--for he cannot deny himself." What he cannot deny is "the faith and love that are in Christ Jesus" and that makes him who he is.
Boring & Craddock in their People's New Testament Commentary also deal with this tension between denial and faithfulness, "God's faithfulness is not dependent on ours; God's acceptance of us is based on who God is, not on who we are or what we have done." They assert that "this paradox permeates the whole New Testament" and offer the examples of Philippians 2:12-13 and Revelation 20:11-15. I would add that there's also a lot of undeserved acceptance in the Old Testament as well.