When I write to Sen. Sinema asking her to support filibuster reform, she returns a letter filled with landmark dates of this history of the filibuster. It reminds me of a poor history teacher; one who believes history is about memorizing the dates of important events without understanding what the events were about.
The filibuster was permitted by Senate rule beginning early in the 19th century as a courtesy to allow delay on votes while proponents of the bill on the floor rounded up missing Senators to come to the floor to vote. Rather than arbitrarily cut off debate, the minority present in the Senate was allowed to speak indefinitely in opposition to a bill while their cohorts sought out missing Senators and brought them in to attend the vote. There were no cell phones, pagers, automobiles, or jet planes. Messengers had to be sent out on foot or horseback and the returning Senator rode horseback or carriage to get to the Capitol for the vote. Even with these communication and transportation impediments, the filibuster rule required that those opposing the bill must have sufficient manpower (they were all men) to occupy the floor and speak until their compatriots arrived. Without that bare minimum of support, a vote would be taken and the bill passed without waiting for the arrival of missing senators. The burden was on the minority to prevent a vote by mustering enough support for their minority position to hold the floor.
Throughout all the dates Sen. Sinema recites, the filibuster has been changed until we have reached the point that the burden has shifted from the minority to the majority to produce a super-majority of 60 votes to move any bill forward. The filibuster has shifted from courtesy to an obstructive device.