This is a classic illogical proposition. You are denying the antecedent. Just because you can’t see the triangles doesn’t mean that they are there. It is a necessary but not sufficient condition to state that you may have triangles if you do not see the triangles. If you have triangles, you will not see them. But just because you don’t see them won’t mean that you have them. Because nobody sees them. Logic won’t save you!