I am doing the research using the panel data. My confusions follow.

Y=x1+x2: X1 sig, but X2 insig.

however, when interaction is put into the model

Y=X1+X2+X1X2, all (X1, X2, X1*X2) have significant coefficients.

Anyone can help to explain the insig. X2 in first model?

really appreciate!!