Strange is far more confident in his guilt trip than he really should be. After all, he already had a prior conversation with the brat and it...well, it didn't go terribly, but it certainly gave Strange more hope that Steven would make the right choice than he had before.

"Agreed. However, if Steven takes his place as the catalyst of his own free will or someone else forces the kid into the role, then the terms are still in place."

This is an alliance, not a legal contract, and yet Strange can't help but be as legalistic and as definite as possible. A side-effect of dealing with the fae, he would assume.