System Summary
An advantage of opening 1NT is that it makes opponents' life difficult.
A disadvantage is that we prefer a major suit if we have a fit. So, we have artificial mechanisms:
With a 5+ card major responder uses a transfer.
With a 4-card major responder uses Stayman.
But there is no mechanism to find a fit when responder has a 3-card major.
THE ASSUMPTION IS THAT OPENER DOES NOT HAVE A 5-CARD MAJOR.
It is worth noting that if opener has a 5-card suit, then the most likely number of cards responder has in the suit is three.