Consent is the cornerstone of everything we do. 

Touching someone without their authentic consent, especially in a context like this where restraint is involved, is legally assault in many jurisdictions.

Depending on where you live, consent may not be a viable defense against assault charges in a court of law. See BDSM and the Law for more.

Get used to asking for consent. With practice, it becomes second nature.

Agreement is not the same thing as consent.  Consent is a type of agreement, held to a much higher set of standards:

Consent Must be Authentic, Informed, and Explicit