While there are strategic advantages to that - if he wins, it’ll feel more like a mandate that will justify whatever horrifying shit his administration intends to do and if he loses, it’s an instant objection - I tend to think that the real foundation of this whole attitude is just Trump’s delusional narcissism.
Trump’s reality isn’t rooted in actual objective reality. It’s based on himself and himself alone - if he believes it, then, to him, it is and can only be true, and he believes whatever serves to assuage the squalling demands of his titanic ego and his childish greed and need for attention.
I have no doubt that in the fantasy universe in which he actually lives, he really can’t possibly lose. It’s just in the real universe - the one the rest of us live in but he does not - that he can (and hopefully will) lose.
“Democracy is the theory that the common people know what they want and deserve to get it, good and hard.” - H.L. Mencken