When holding a 4-3-3-3 or 3-4-3-3 distribution, it is best to bid notrump rather than search for a 4-4 major suit fit.  Since your partner opened 1NT showing one of the following shapes: 2-3-3-5, 2-3-4-4 or 3-3-3-4, at most either of you have is one doubleton.  The ruffing value in the 4-4 major suit fit no longer applies.

Remember this shape is the “Ugly Duckling” shape which means you want to downgrade the hand.  In other words, holding an Ugly Duckling hand with 8 points – don’t invite…with 10 points, just invite.

via Play Better Bridge.