For example, say you control Prize Wall, which has "{U}, {T}: You get {TK}." You activate Sole Performer to get {T}{T}. You then activate Prize Wall, spending {U} and one of the {T}s you got from Sole Performer. You could then activate Prize Wall again, spending another {U} and the other {T}. Prize Wall itself is still untapped at this point. You can then activate Prize Wall a third time, spending a third {U} and finally actually tapping Prize Wall.