It's amazing Whitesnake were as successful as they were; the group never could stabilize its lineup. While recording Slip of the Tongue -- the crucial follow-up to 1987's self-titled effort, which went platinum eight times over -- Whitesnake lost twin guitarists Vivian Campbell and Adrian Vandenberg. Gun-for-hire Steve Vai stepped in, allowing the group to not miss a beat. Selling in excess of 4,000,000 copies, Slip of the Tongue was yet another pop metal blockbuster for David Coverdale and company.