The practicalities of the commercial world, with which the trademark laws deal¹
Exhibit A: Musical group Cracker.
Exhibit B: Musical performer Uncle Kracker.
Apparently they can and do coexist.
¹Witco Chem. Co. v. Whitfield Chem. Co., 418 F.2d 1403, 1405, 164 U.S.P.Q. 43, 44-45 (C.C.P.A. 1969), aff’g 153 U.S.P.Q. 412 (T.T.A.B. 1967)
²Why the heck, you ask? I saw a song by Cracker on XM Radio and my mind just started whirring . . .