To add on to Cindy's excellent answer, I want to point out that while VBA normally has safeguards to coerce the values when assigning to a Boolean data type, this can be circumvented. Basically, if you write a random value to a memory address that's not yours, then you should expected undefined behavior.
To help demonstrate this, we'll (ab)use LSet which essentially allow us to copy the value without actually assigning.
Private Type t1
b As Boolean
End Type
Private Type t2
i As Integer
End Type
Private Sub Demo()
Dim i1 As t2
Dim b1 As t1
Dim b As Boolean
i1.i = 1
LSet b1 = i1
b = b1.b
Debug.Print b, b1.b, i1.i
Debug.Print CInt(b), CInt(b1.b), i1.i
End Sub
Note the line b = b1.b is basically equivalent to what we did in the OP code
X = Selection.Cells(1).FitText
That is, assigning a Boolean to another Boolean. However, because I wrote to the b1.b using LSet, bypassing VBA runtime checks, it doesn't get coerced. When reading the Boolean, VBA does implicitly coerce it into either True or False, which seems misleading but is correct because any falsy results is one that equals 0 (aka False), and any truthy results is one that doesn't. Note that the negative for truthy means that both 1 and -1 are truthy.
Had I assigned the 1 to a Boolean variable directly, VBA would have had coerced it into -1/True and thus there'd be no problem. But evidently with FitText or LSet, we are basically writing to the memory address in an uncontrolled fashion, so that VBA start to behave strangely with this particular variable since it expects the Boolean variable to already had its contents coerced but wasn't.
