Option Explicit
Private Sub Worksheet_Activate()
Dim T() As Variant, N As Integer
ReDim T(1 To ThisWorkbook.Sheets.Count, 1 To 1)
For N = 1 To UBound(T, 1)
T(N, 1) = Sheets(N).Name
Next N
Me.[A2].Resize(10000).ClearContents
Me.[A2].Resize(UBound(T)).Value = T
End Sub