The die could have been filled with grease, but this is a common area of weakness on Lincoln Memorial cents because of metal flow into the shoulder area of Lincoln on the obverse.
Burt, it would really, really, really help if you would tell us what we are supposed to see. Yes, that is a 1955 Lincoln cent. What else would you like to know? Chris
This whole area of the coin often sees missing letters, also at "States" and "Of". Grease filled or simple die deterioration are common. Also missing will be the inner roof in the last chamber of the building.
deteriorated die or grease filled die could have caused it. Very common error though, not worth more than face. I see them regularly in boxes of pennies (or cents for all those grammar freaks lol)