Speaking in generic terms, the ability to perform in a 121 environment encompasses exactly what it sounds like: the ability to act, dress, and operate as an airline professional. Punctuality, appearance, behavior, and professional performance. That will include the ability to function as an airline pilot, to study, to learn, and to operate to ATP standards at all times. It means the ability to show up at the aircraft on time, and get the airplane out on schedule. For many, that also means the ability to manage a commuting schedule, to live within one's means, to operate as a crew member, to get along in the cockpit, as well as with the customer, with mechanics, gate agents, and others, and to fit in.

The airline may have thousands of personnel, and pilots. Operating in a 121 environment is best done in a way that the Chief Pilot never knows your name. About 10% of the pilots occupy 90% of the Chief Pilots attention. Don't be one of that 10%.