Supporting actors or character actors can make a good movie a great one. The scene in Absence of Malice is made by several supporting actors of which not the least was Wilfred Brimley.
They never get the girl and they may not be that good looking and sometimes they have the best lines. One example is Eve Arden's role as Mildred Pierce's friend when the two of them are talking about Mildred's daughter the Eve Arden's character says "I think alligators have the right idea, they eat their young."
The big studios like MGM and Warner Brothers had a great group of character actors which when you watch those movie from the 30ths, 40ths and 50ths.
Great movies like Casablanca, The Searchers, and even Gone with the Wind has great cast of character actors. Watch for them.